introduction to chem

8/6/2019 Introduction to Chem

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2.1 Mixtures

A mixture is a substance consisting of two or more substances mixed together but the

components are not chemically bonded (physical combination). The mixture can be

separated by physical separation techniques such as evaporation, distillation,

magnetism etc...

Types of Mixtures

1. Homogenous: mixture where the composition is uniform through

EG: dissolving salt in water (any time there is a solvent and solute), air

2. Heterogeneous: mixture where the components are easily identified (not uniform

throughout).

EG: potting mix

2.2 Elements and Compounds Mixtures can be separated in to pure substances. Pure substances are either elements or

compounds.

Elements

They cannot be separated any further. They are made up of billions of the same type of

atom. EG: oxygen, magnesium, neon, nitrogen, barium etc... Elements known to exist are

found on the periodic table.

Compounds

Are made of different atoms of different elements that are joined (or compounded)

together. Atoms are joined together in a fixed ratio.

EG: magnesium oxide, water, sodium hydroxide, barium chloride. The process of

breaking down compounds is called ___________________________.



2.2The Periodic Table

The periodic table of elements is a tabular display of elements. They have rows and

columns which represent different.

Periods

y These are the rows running across the table.

y All of the elements in the same row have the samenumber of atomic orbitals.

y EG: Elements in the first row (first period) has one

orbit for its electrons. Second period has 2 orbits

etc...

Groups

y These are the columns that go from top to

bottom.

y Elements in a group have the same number

of electrons in its outer orbits.

y EG: Elements in the first group have one

electron in its outer shell, second group has 2

electrons in its outer shell.

Hydrogen and helium

y Hydrogen can either have one electron missing (H+) or

one extra (H-).

y Helium has only 2 electrons in its outer shell but is

grouped with the inert gases (group VIII)

Reading the Periodic Table



2.3 Energy Levels

2.3.1 Atomic Structure and Orbits

You know that an atom consists of 3 types of subatomic

particles:

1. Neutrons

2. Protons (+vely charged particles)

3. Electrons (-vely charged particles)

*N o. of Protons = N o. of Electrons

Electrons & Orbits

y Electrons orbit in layers or shells. AKA

energy levels.

y Each shell is filled with a maximum number

of electrons before the next layer starts to

fill.

y Maximum number of electrons in each shell

is given by: 2n2, where n is the shell

number.

- 1st shell: 2 x 12 = 2

- 2nd shell: 2 x 22 = 8

- 3rd shell: 2 x 33= 18

Etc....

Write down the electron configuration for the following elements:

1. Boron:

2. Nitrogen:

3. Aluminium:

4. Silicon:

5. Phosphorus:

6. Argon:

7. Selenium:

8. Xenon:

9. Strontium:

10. Lead:

2.3.2 Valency

Valency is the number of chemicalbonds the atom of a certain element

can form. It is measured by the

number of electrons which an atom

can give, take, or share to form a

chemical compound.

It is related to the number of spaces

left in an atoms electron shell.



2.4 Naming Compounds

1. Ionic compounds

Ionic compounds are made up of a cation (usually metal) and anion (non -metal).

General rule:

name of cation + name of anion, suffix 'ide'

EG:

y NaCl: sodium (cation, Na+) followed by chlorine (anion, Cl-)changed with the

suffix 'ide' = sodium chloride

y CaO: Calcium Oxide

y Li3N: Lithium Nitride

2. Non-metals

Where atoms (non metal) of different elements combine in more than one ratio, the

relative numbers present in each compound are indicated by the prefixes.

Mono 1 Tri 3 Pent 5 Hept 7 Non 9

Di 2 Tetr 4 Hex 6 Oct 8 Dec 10

EG:

y NO2: Nitrogen Dioxide

y N2O4: Dinitrogen tetroxides

y N205: Dinitrogenpentoxide

3. Cation/Anion + Polyatomic Ion

Sometimes one of the ions is a compound (polyatomic ion). They are also known as

chemical radicals. A chemical radical is a group of atoms which tend to stay together

when the compounds reacts with another compound.

List of common radicals below:

Name of radical Valency Formula of radical as it appears in

chemical compounds

Ammonium +1 NH4+

Carbonate -1

CO32-

Sulfate -2 SO42-

Sulfide -2 S032-

Nitrate -1 NO32-

Hydroxide -1 OH-

Permanganate -1 MnO4-

Nitrite -1 NO2-

EG: Na2SO4: Sodium Sulfate



2.5 Writing Chemical Formulae

1. Sodium Oxide

2. Magnesium Chloride

3. Zinc Oxide

4. Aluminium Carbonate

5.

Mercury (II)N

itrate6. Barium Carbonate

7. Lead (II) Oxide

8. Copper (I) Chloride

9. Silver Nitrate

10. Iron (III)Hydroxide

11. Potassium Flouride

12. Copper Sulfate

13. Ammonium Sulfate

14. Aluminium Phosphate

15. Copper (II) Chloride16. Lithium Acetate

17. Magnesium Nitride

18. Beryllium Oxide

19. Sodium Sulfate

20. Potassium Permanganate

21. Tin Sulfite

22. Ammonium Nitrate

23. Vanadium (V) Flouride

Group Assumed Valency

I +1

II +2

III +3

IV ±4

V -3

VI -2

VII -1

VIII 0

introduction to chem

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