Greetings and kicking off

Greetings

Salutation, I am Tan Chin Han from class 2P4. I am going to share with you what I have learnt, experienced and explored in Science during  my secondary two in HCI.

Declaration

I hereby declare that the start date of my Science Eportfoliois on 3rd of November, 2012. Are you surprised? Actually yes, you should be, and do you know the reason why I have started few months earlier? The reason is that I feel energised after getting a surprisingly good result (A1) in my Science for my overall in Sec 1 (I have not achieved any  A1 in term 1,2,3). Therefore, in order to Ace Science again, I have decided to start it early so as to record things I have learnt in Science into this awesome blog everyday and make it a perfect blog to get high marks!

 

Kicking it off

To kick it off, I will start this blog with 2 videos which explains an easy question but with different answers and opinion : What is Science? (these vdeos does not belong to me, they are interesting videos which I think should be shown)

 

 

 

First progress: Advanced Science revision

 

Phew! After casual talking with my seniors regarding what they had learnt during term 1 for Secondary Two Science, I understand that it was Chemistry that was being taught. I decides to put what I know in the following, with reference to the Science reference book entitled "IGCSE Chemistry" by Bryan Earl and Doug Wilford.

The Atom Structure

Protons: 

 

They are subatomic*  particles with the symbol p or p+.  (subatomic are particles which are smaller than atom)  They are present in the nucleus. The number of Protons in each atom is its atomic number.Its relative mass is 1. Protons determine what elment an atom is. It has a positive charge.

 

Neutron 

The neutron is a subatomic hadron(  composite particle made of quarks held together by the strong force) particle which has the symbol n or n0,it has a slightly larger mass than protons. The number of protons in a nucleus is the atomic number and defines the type of element which the atom forms. Its relative mass is 1.  It has no charges(neutral)

Electrons:

It  is a subatomic particle and has negative elementary electric charge.

It orbits around the nucleus in orbitals which is called shells. It has a relative mass of 1/2000.  The number of elctrons  is its atomic number and it determines the charge of the atom.

 

*HOWEVER, note that the relative mass is not very accurate. After searching the websites for the relative mass, what I have written here is a rounded up relative mass. The actual relative mass(which I sourced from majority of internet research) for proton, neutron and electron is:

Assuming that the neutron has a mass of 1, then the relative masses for elcetrons and protons are:
Neutrons=1
Protons= 0.99862349
Electrons= 0.00054386734/    1/1837
 Protons are aprroximately about 99.86% as massive as Neutron, while electrons are 0.054% as massive as Neutron. Therefore, in kg, the mass is:
Neutron = 1.6749286 x10^-27 kg
Proton = 1.6726231 x 10^-27 kg
Electron = 9.1093897 x 10^-31 kg


Now, lets look at one example of an atom structure. 

 

 

As you can see, the dots surrounding the nucleus are electrons while the nucleus, which contains protons and neutrons, is in the center. The electrons are held within the atom by an electrostatic force of attraction between themselves and the positive charge of protons in the nucleus.

 

Now, lets look at a typical hydrogen atom, it consists of only one electron and a proton in the center:

 Periodic TimeTable

Now, let's revisit our sec 1 topic: the hard-to-memorise periodic timetable.

Here, is a periodic timetable, and it can truly wreck your brains if you want to memorise it:

Now, we will recap what we have learnt about the periodic time table in secondary 1:

The periodic table consists of different types of elements which are arranged in charts and

     it has an arrangement of elements in order of increasing number of protons.

Now, lets scrutinise at the horizontal rows of the peiodic table:

The horizontal rows are called periods.

It is grouped by 1,2,3,4.......

It is grouped by the number of shells.

The elements in the same periods changes slowly from metal to non metal and the sequence is from the left to the right.

Now, lets scrutinidr at the vertical columns of the periodic timetble:

They are called groups.

They are grouped by the number I, II, III, IV, V, VI, VII, 0.

They are grouped according to the number of electrons in the outer shells.

The elements of each group have a similar properties.
The elements circled by an oval with red ink are metalloids. Metalloids are elements that have some properties of metals and some of non metals. Here is the picture:

 

Relaxation

I sincerely hope that no one gets bored by looking at this chunk of Science stuff, therefore I will put in a video(not owned by me) on periodic time table to liven up the whole blog.

This is called the element's song, by Tom Lehrer. He is a  singer-songwriter, satirist, pianist, and mathematician, he is quite funny and I hope you will like the fast paced song, the ELEMENT'S SONG!

 

 Back to work- the periodic table

Well, after a bit of fun, we will now revert back to our topic. In Secondary one, I initially thought that I had learnt everything about the periodic table. It turns out I was wrong. Now, I saw an interesting word in how the periodic table is grouped by- shells.

 Intriudged and confused, I decided to look upon the internet to find out more information about shells.I have searched the meaning of shells in the dictionary and here is its scientific meaning:

a. Any of the set of hypothetical spherical surfaces centered on the nucleus of an atom that contain the orbitals of electrons having the same principal quantum number.

b. An analogous pattern of protons and neutrons within a nucleus.

 

 

After researching more about it, I think that it can also be called electron shell. It is thought of as an orbit followed by electrons around an atom's nucleus.

 

Also, I found out that:

Shells can only contain a fixed number of electrons. In the periodic table(periods), the number of electrons a shell contain is subsequent to the periodic number, in dupet structure, for example, the 1st shell contains 2 electron (a duplet structure).

 

Also, I have also found out that (about shells):

The electron configuration or organisation of electrons orbiting neutral atoms shows a recurring pattern or periodicity.

The electrons occupy a series of electron shells (numbered shell 1, shell 2, and so on). Each shell consists of one or more subshells .

As atomic number increases, electrons progressively fill these shells and subshells more or less.

Number of electrons in the last shell will be decided by group number.

 

The first energy level can hold up to 2 electrons, 2nd can hold up to 8 and the third can hold up by 18.

Back to periodic

In Science, actually, periodic tables have 18 groups, unlike the 7+0 groups that we are learning. Here is a picture which numbers them into 18 groups:

 

As we have only covered 7, plus 0 groups, I am unable to provide information about this. However, after researching on it, generally, I found out the number of groups and what is contains. It is quite complicated:

Group 1: the alkali metals or lithium family

Group 2: Alkaline earth metals or beryllium family

Group 3:the scandium family, which consist of rare earth elements  and actinides

Group 4: the titanium family

Group 5: vanadium family

Group 6: the chromium family

Group 7: the manganese family

Group 8: the iron family

Group 9: the cobalt family

Group 10: the nickel family

Group 11: the copper family

Group 12: the zinc family

Group 13: the triel or boron family

Group 14: the tetrels or carbon family

Group 15: the pnictogens or nitrogen family

Group 16: the chalcogens or oxygen family

Group 17: the halogens or fluorin e family

Group 18(0): the noble gases, helium family or neon family

END

Now, thats a bit overwhelming, don't you think so?

 

Atomic numbers and mass numbers

We are now still on the periodic table, now, let's look at the atomic and mass numbers of an element:

 

 

 As you can see, atomic number is known as Z, whereas Mass number is known as A.

 

Isotopes

 

What are isotopes?

Isotopes are atoms of the same element which have different numbers of neutrons. Isotopes behaves in the same way during chemical reactions  and the only effect of the extra neutrons is to alter the mass of the atom and the properties which depend on it, such as density. For example, lets look at two random isotopes of the same atom:

In short, lets look at the differences and similarities:

Differences: physical properties, mass number

similarities: chemical properties, atomic number

 

Types of isotopes:

There are two types of isotopes: unstable and stable.

Unstable isotopes, which is because of the extra neutrons in their nucleus are radioactive and are called radioisotopes.(clarification:I am not sure whether this types of isotopes are tested in sec2, as I got the information from secondary four sources.) For example, uranium -235 which is used as a source of power in nuclear reactors and cobalt -60 which is used in radiotherapy are both radioisotopes.

 

INTERESTING FACT: How do we know that isotopes exist? They were first dicovered by scientists using apparatus called a mass spectrometer.

 

The octet structure

The octet structure states that atoms that have low atomic number tend to have eight eletrons in their valence shells.

 

Ionic bonding: they are formed through electrostatic atttraction between two oppositely charged atom.

 

 Pure ionic bonding cannot exist. Positive: fewer electrons than protons, known as cations.

Negative: anion, an ion with more electrons than protons.Ionic bonding is betwwen metals and non metals.

 

Few of these examples are: NaCI, Na is 2.8.1, CL is 2.8.7 If Na loses one electron it becomes Na+, whereas if CL gains one electron it will become C1-

The charges of an ion is the number of electrons needed to be gained or lost to get a stable octet srucute.

 

The chages are:

Group 1
All are 1+
Group 2
All are 2+
Group 3
Sc 3+	Y 3+	La 3+	Ac 3+
Group 4
Ti 4+ 3+	Zr 4+	Hf 4+
Group 5
V 5+ 4+	Nb 5+ 3+	Ta 5+
Group 6
Cr 3+ 2+	Mo 6+	W 6+
Group 7
Mn 2+ 4+	Tc 7+	Re 7+
Group 8
Fe 3+ 2+	Ru 3+ 4+	Os 4+
Group 9
Co 2+ 3+	Rh 3+	Ir 4+
Group 10
Ni 2+ 3+	Pd 2+ 4+	Pt 4+ 2+
Group 11
Cu 2+ 1+	Ag 1+	Au 3+ 1+
Group 12
Zn 2+	Cd 2+	Hg 2+ 1+
Group 13
Al 3+	Ga 3+	In 3+	Tl 1+ 3+
Group 14
Ge 4+	Sn 4+ 2+	Pb 2+ 4+
Group 15
Sb 3+ 5+	Bi 3+ 5+
Group 16
Po 2+ 4+

 

The name of a compound is its cation name plus its anioon name.

Let me show you a video of ionic bonding(does not belongs to me)

 

 

 

 Covalent bonding- It is a chemical bonding with involves the sharing of pairs of electrons between atoms.

The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding.

 It is for non metal compounds only . Each atom contributes 1/2/3 atoms to the bond.

 

Lets see a video of covalent bonding (it does not belong to me)

 

Lets see a compound covalent bonding

carbon needs 4 more valence electron, 4 hydrgogen atoms are called in

4 plus 4 equals 8

 

What is valency? It is the number of electrons an atom uses to bond.

Molecules can be a cube or a hexagon, as long as its a lattice structure(lattice means crystal structure)

The structure of a molecule is specified by the identity of its constituent atoms and the sequence in which they are joined together. It is described by the combination of the nulcei and electrons.

Giant metallic-

 

closely packed atom

They have a high density as grains are pushed tightly together. They are malleable, have good electric conductivity.

 

Giant covalent

Structure of (example of giant covalent)diamond:

 

Carbon has an electronic arrangement of 2,4. In diamond, each carbon shares electrons with four other carbon atoms - forming four single bonds.It continues on and on in three dimensions. It is not a molecule, because the number of atoms joined up in a real diamond is completely variable - depending on the size of the crystal.

Properties
-Hard, due to the strong covalent bonds operating in three dimensions.
-High melting point(almost 4000 degree celsius)  due to the need to break very strong carbon-carbon covalent bonds throughout the structure before melting occurs.
-Does not conduct electricity- all electrons are held tightly together, which means that they are not free to move.

Giant ionic

Giant ionic is caused because of ionic bonding.

Structure:  cube like

 

High melting point and boiling point( strong chemical bond exist between all the ions)

Electricity conductor(they conduct electricity when dissolved in an aqueous solution or when moltens.( as the ions will seperate and are free to move.)

 

 

Now, lets move on to simple molecular, this is a picture of a simple molecule:

What is molecule?

Ans: The strucutre of a non metallic element  or compound,  in which groups of atoms are joined together by convalent bonds is known as a molecule.

 

More about it(molecules):

 Non metal molecules are often made up of two identical atoms convalently bonded together, e.g.: oxygen, hydrogen and nitrogen.

 

Molecules are mostly non metallic, and have strong covalent bonds. Also, although the covalent bonds within the molecules are very strong the molecules are held together by weak intermolecular forces. As the molecules can be parted easily(as most are non solid and have weak van der waals force to keep them together), simple molecular substances are not very hard or strong and have low lmelting and boiling point. As such, most simple molecular substances are either gas or liquid. Also, they do not normally dissolve in water and do not conduct electricity as they do not have ions. Simple molecular solids such as ice, tend to dissolve in organic solvents and melt easily.

 

So, to recap, these are the properties of the molecule:

Non conductor of electricity

Low melting and boiling point

Not strong, soft.

 

 To relax , please go to this website to watch a video about molecules: http://videos.howstuffworks.com/science/molecule-videos-playlist.htm#video-29390

This website contains lots of interesting videos.

 

 

Chemical equations

A chemical equation consists of the chemical formulas of the the starting substances of the products

CH₄+ 2 O₂ CO₂+ 2 H₂O

This equation would be read as "CH four plus two O two yields CO two and two H two O."

Ok, lets have another example. Mg, which has 3 shells and 2 outer electrons, and 2 CL, which each has 3 shells and 7 outer electrons. To make it stable when combined, we need to have 8 outer electrons when combined. Thereore, by transfering one outer electrons from Mg to each of the two CL, 7 +1= 8, thus having the equation  MgCl2.

These are a list of anions and cations, from a reference website: http://myweb.astate.edu/mdraganj/cationanion.html

Common Cations: (ions grouped by charge)

Name	Formula	Other name(s)
Aluminum	Al+3
Ammonium	NH4+
Barium	Ba+2
Calcium	Ca+2
Chromium(II)	Cr+2	Chromous
Chromium(III)	Cr+3	Chromic
Copper(I)	Cu+	Cuprous
Copper(II)	Cu+2	Cupric
Iron(II)	Fe+2	Ferrous
Iron(III)	Fe+3	Ferric
Hydrogen	H+
Hydronium	H3O+
Lead(II)	Pb+2
Lithium	Li+
Magnesium	Mg+2
Manganese(II)	Mn+2	Manganous
Manganese(III)	Mn+3	Manganic
Mercury(I)	Hg2+2	Mercurous
Mercury(II)	Hg+2	Mercuric
Nitronium	NO2+
Potassium	K+
Silver	Ag+
Sodium	Na+
Strontium	Sr+2
Tin(II)	Sn+2	Stannous
Tin(IV)	Sn+4	Stannic
Zinc	Zn+2

Common Anions: (ions grouped by charge) (anions grouped by periodic position)

Simple ions:
Hydride	H-	Oxide	O2-
Fluoride	F-	Sulfide	S2-
Chloride	Cl-	Nitride	N3-
Bromide	Br-
Iodide	I-
Oxoanions:
Arsenate	AsO43-	Phosphate	PO43-
Arsenite	AsO33-	Hydrogen phosphate	HPO42-
		Dihydrogen phosphate	H2PO4-
Sulfate	SO42-	Nitrate	NO3-
Hydrogen sulfate	HSO4-	Nitrite	NO2-
Thiosulfate	S2O32-
Sulfite	SO32-
Perchlorate	ClO4-	Iodate	IO3-
Chlorate	ClO3-	Bromate	BrO3-
Chlorite	ClO2-
Hypochlorite	OCl-	Hypobromite	OBr-
Carbonate	CO32-	Chromate	CrO42-
Hydrogen carbonate or Bicarbonate	HCO3-	Dichromate	Cr2O72-
Anions from Organic Acids:
Acetate	CH3COO-	formate	HCOO-
Others:
Cyanide	CN-	Amide	NH2-
Cyanate	OCN-	Peroxide	O22-
Thiocyanate	SCN-	Oxalate	C2O42-
Hydroxide	OH-	Permanganate

 ACIDS

Whats is acid?

 The word acid means sour and all acids posses this property, they are also soluble in water and corrosive.

 

Alkalis:

They are very different from acids, they are the chemical opposite of acids The will remove the sharp taste from acid and they have a soapy feeling. Some coomon alkaline substances are: toothpaste bleach etc. It would be too dangerous to find out if it was acidic(if its concentrated it may dissolve your whole mouth), therefore chemists use substances called indicators which change colour when they are added to acids or alkalis. Many indicators are dyes which has been extracted from natural sources. Litmus is a purple dye which has been extracted from lichens. It turns red when it is added to an acid and turns blue when added to an alkalis.

 

Lets see the colour changes in different dyes:

Blue litmus:   acid: red   alkaline solution:blue

Methyl orange: Acid: Pink Alkaline:Yellow

Methyl red: acid: red   Alkaline: yellow

Phenolphtalein: acid: colourless   alkaline:pink

Red litmus  acid:red   alkaline:  blue

Thes indicators tell chemists whether a substance is acid or an alkaline. To obtain an idea of how acidic or alkaline a substance is, we need to use a universal indicator. It has a mixture of other many indicators  and the colour shown by this indicator can be matched against a PH scale:

 

 

 Lets lighten this mudane and boring lesson about science! Now, you have already seen the element song, thinking that its funky and funny enough, now I present to you something more hilarious, more funky, more eccentric,

 

 Now, ladies and Gentleman, behold the song: Acids And Bases Have Two Different Faces

Please listen to it, it will surely lighten this whole lesson up. We gurrantee you that this song need no parental guidance (as its really safe for kids to watch).

 

Now, lt's my turn to share with you more interesting facts of acids and chemistry:

Bee stings are acidic while wasp stings are alkaline.

Hydrofluoric acid is so corrosive that it will dissolve glass. Although it is corrosive, hydrofluoric acid is considered to be a 'weak acid'.

Lightning strikes produce O₃, which is ozone, and strengthen the ozone layer of the atmosphere.

Although oxygen gas is colorless, the liquid and solid forms of oxygen are blue.

 

 

 

ACIDS

Back to acid!

Theories of acid and bases.

There have been many attempts to define the difference between acids and bases. There is a theory on the acid and bases, known as the Bronsted-Lowry theory.

 

The theory defined that:

an acid as an H+ ion (or proton donor)

a base as as H+ ion9or propton acceptor)

The theory explains why a pure acid behaves differently from its aqueous solution, since for an acid to behave as an H+ ion donor it must have another substance present to accept the H+ io. So the water, in the aqueous acid solution, is behaving as a Bronsted-Lowry base and accepting an H+ ion.

 

Relative strengths of acid and bases.

The relative strength of an acid is found by comparing one acid with another. The strength of any acid depends on how many molecules dissociate when the acid is dissolved in water.  The relaive strengeth of a base is found by comparing one base with another and is again depenedent upon the dissocaition of the base in aqueous solution.

 

Strong and weak acid

A typical strong acid is hydrochloric acid. It is formed by dissolving hydrogen chloride gas in water. In hydrogen chloride gas in water. In hydrochloric acid the ions formed seperate completely.For hydrochloric acid all the hydrogen chloride molecules break up to form H+ ions and Cl- inos. Any acid that behaves this way is termed a strong acid.A weak acid such as ethanoic acid which is formed in vinegar, produces a few hydrogen ions when it dissolves in water compared with a strong acid of the sam Concentration.  Solutions of weak acids are poorer conductors of electricity and have slower reactions with metal bases and metal carbonates while storng acids are good conductors of electricity and have faster reaction.

                                                              Neutralsing an acid

A common situation involving neutralisation of an acid is when you suffer from indigestion. This is caused by a build up of acid in your stomach. You will treat it by taking a remedy containing substance that will react react with and neutralise the acid. In the lab, if you want to neutralise acid such as hydrochloric acid you can use alkali. If the PH of the acid is measured as some sodium hydroxide solution is added to it, the PH increases. If equal volumes of the same concentration of hydrochloric acid and sodium hydroxide are added to one another, the resulting solutionis found to have a PH of 7, which means that the acid has been neutralised and a neutral solution has been formed.

 

Salts:

A notmal salt is a compound that has been formed when all the hydrogen ions of an acid  have been replaced by metal ions or by ammonium ions.

 

Ammonium chloride: in torch batteries

To produce soluble salts, we can use acid plus metal.This method can only be used with the less reactive metal.

 

Acid plus carbomnate

This method can be used with any metal carbonates and any acid, provided that the salt produced is soluble.

 

Acid+alkali: for preparing the salts of very reactive metals.

 

Ammonium nitrate: fertilisers

 

Calcium sulfate: for making plaster bosrds

 

The test for different salts is known as spot tests

 

In conclusion, these are a  note of a few important things you must know about the acid:

Weak acid produces a low concentration of H+(aq) in water solution while a weak akali will produce a low concentration of OH-(aq) in water solution.

Base is a substance which neutralises acid.

Final revision of the Mock term one materials

One more thing to learn and we will finish the "term one" topics which I gathered from my upper sec seniors. I repeat, this is not the actual things that I have learnt in term 1. I did this INTRODUCTORY PART during  the holiday through internet researching and  reading reference books.

 

Ok, now for the last thing that is important to know:  Chemical equations.

 

A chemical equation:

 is the symbolic representation of a chemical reaction where the reactant entities are given on the left hand side and the product entities on the right hand side.

An arrow sign, ->, is known as yield  + is known as and.

 

An example is:

The formula for the burning of methane:

CH₄+ 2 O₂ CO₂+ 2 H₂O

We can read this equation as "CH four plus two O two yields CO two and two H two O."

Balancing chemical equations:
The law of conservation of mass dictates the quantity of each element does not change in a chemical reaction. Therefore,  a chemical equation must represent the same quantity of the element. Also, the same charge must be present on both sides of the balanced equation. Also, they must also be an equal number of atoms on opposite sides.

There! This is the End of the simplified early holiday version of  Sec 2 term 1 topic. It does not matter whether the same thing will be taught during the term as what I have learnt will always be with me.

  

School is starting soon! And I will update the Science blog everyday with what I have learnt during the class.

 

Goodbye!