CHEMISTRY TOPIC 1- Atomic Structure and the Periodic Table

Topic 1 of Chemistry, in paper 1 of AQA

Protons

+1 charge

+1 mass

Found in the nucleus of an atom

Discovered by Ernest Rutherford in 1919

Electrons

-1 charge

+0 mass (negligible)

Found in the electron shells

Discovered by J.J. Thomson in 1897

Neutrons

+0 charge

+1 mass

Found in the nucleus of an atom

Discovered by James Chadwick in 1932

Radius of a nucleus

1×10^-14 metres

Overall charge of a normal atom

0- neutral since the number of protons is the same as the number of electrons

Atomic number

Aka proton number

Bottom number

Tells how many protons there are

Mass number

Top number

Mass of an element

Sum of the number of protons and neutrons

Isotope

Atom of the same element but with a different number of protons

Same atomic number

Different mass number due to different amount of neutrons

Relative Atomic Mass equation (Ar)

sum of (isotope abundance * isotope mass number) / sum of abundances of all isotopes

Element

Compound

Mixture

Substance of only one atom type

Substance of 2+ different atoms chemically bonded

Substance of 2+ different atoms together with no chemical bonds

Diatomic

Element that exists as two atoms bonded together

Inert

Chemically unreactive

Soluble and Insoluble

Soluble substances dissolve in water

Insoluble substances don’t dissolve in water

Chromatography Practical Method

1. Draw line with pencil near bottom of filter paper (pencil is insoluble)

2. Add ink spot on pencil line and put bottom of sheet in beaker of solvent (water, ethanol…)

3. Put lid on container (prevent evaporation)

4. Solvent will travel up the paper, bringing and separating the ink into its components based on their different affinities to the paper (insoluble dyes in the ink will stay on pencil line)

5. Take paper out of beaker once the solvent is nearly at the top

Stationary and Mobile Phase in Chromatography

Stationary- Chromatography paper

Mobile- Solvent that moves through stationary phase and carries mixture

Filtration

Separate an insoluble solid from a liquid mixture

Also used in purification in removing solid impurities

Evaporation to Separate Soluble Solid from Solution Method

1. Pour solution into evaporating dish on tripod with gauze mat

2. Heat dish using bunsen burner below (or with beaker of boiling water heated by bunsen burner) - solvent will evaporate and solution will increase in concentration

3. Eventually, crystals will form. Keep heating the dish until only dry crystals remain

Crystallisation to Separate Soluble Solids from Solution Method

1. Pour solution into evaporating dish and gently heat (some will evaporate and increase concentration)

2. Once some is evaporated OR crystals start to form, remove dish from heat and leave solution to cool

3. The salt should form crystals as it becomes insoluble in cold, highly concentrated solution

4. Filter crystals out of solution and leave them in a warm place to dry (drying oven, desiccator…)

Simple Distillation Method

Used to purify liquids by heating and cooling (separates liquid from a solution)

1. Heat solution- part with lowest boiling point will evaporate first

2. Vapour rises to top of flask and travels down condenser where is cools, condenses and is collected in a beaker

3. Rest of solution remains in flask

   Only very useful for separating mixtures made of liquids with very different boiling points

Fractional Distillation Method

Used to separate mixtures made of liquids with close boiling points

1. Put mixture in flask and attach fractionating column on top and heat

2. Liquids will evaporate at different temperatures due to varying boiling points

3. Lowest boiling point liquid evaporates first. When thermometer reads the liquid’s boiling point, it has reached top of column

4. Other liquids may start to evaporate, but the column is cooler towards top so they won’t fully make it up while the other liquid is at the top

5. when all of first liquid is collected, increase temperature until the next liquid reaches the top and repeat until all liquids are separated

   The glass rods n the fractionating column provide more surface area for the liquids to condense on

Plum Pudding Model

1897 by JJ Thompson

Ball of positive charge with negative electrons inside

Alpha Scattering Experiment + Atomic/Nuclear Model

1909 by Ernest Rutherford and student Marsden

Fired positive alpha particles (helium nucleus) at thin gold sheet

Expected for particles to pass straight through or slight deflection- plum pudding model showed positive charge as spread out in atom

More deflected than expected and some were deflected backwards.

This proved there was a small concentrated positive nucleus with most of the mass while electrons surrounded it. Shows most of atom is empty space

When nucleus hit gold sheet, atoms deflected

Improved Nuclear Model

1913- Niels Bohr suggested electrons orbit nucleus in fixed shells in fixed distance from nucleus

Order of Particles’ Discovery

Earliest → Latest

Electrons

Protons

Neutrons

Structure of Atom/Electron Shells

Closest electron shells filled first

1st electron shell: 2 electrons

2nd electron shell: 8 electrons

3rd electron shell: 8 electrons

etc.

Electronic configurations shown as 2:8:8

Electronic Structure of Carbon

2:4

Carbon has Atomic number of 6, so has 6 protons

Number of protons = Number of electrons

So 6 electrons

Only 2 electrons on first shell, and rest are on 2nd shell

Electronic Structure of Chlorine

2:8:7

Chlorine has Atomic number of 17, so has 17 protons

Number of protons = Number of electrons

So 17 electrons

Only 2 electrons on first shell and 8 on second shell

Leaves 7 more electrons which all fit on 3rd shell

Mendeleev’s Table of Elements

1869- Dmitri Mendeleev

50 known elements into Table of Elements

Organised based on atomic mass but also in order based on properties

Included gaps for undiscovered elements with gaps in correct spaces dependant on their properties

Modern Periodic Table

Metals on left, Non-metals on right

Elements in order of increasing atomic number

Periods- rows

Groups- vertical columns organised based on properties e.g. alkali metals, noble gases and halogens

Groups also determine number of electrons in outer shell e.g. group 1 elements have 1 electron in outer shell (group 0 elements have full outer shells)

Alkali Metals

Group 1 of Periodic Table

Reactive; Soft; Low density; Metals

Have 1 electron in outer shell

Form +1 ions (lose 1 electron to make full outer shell)

Trends as you go down Group 1:

Reactivity increases

Lower melting + boiling points

Higher atomic mass

When reacted with water, produce hydrogen

When reacted with chlorine, produce salt

When reacted with oxygen, produce metal oxide

Halogens

Group 7 of Periodic Table

Reactive; Non-metal; Diatomic

Have 7 electrons in outer shell

Form -1 ions (gain 1 electron to make full outer shell)

Trends as you go down Group 7:

Reactivity decreases

Higher melting + boiling points

Higher atomic mass

More reactive halogens displace less reactive ones (e.g. fluorine would displace chlorine and any of the other halogens in a reaction)

Properties of each Halogen

Fluorine:

Yellow gas; Very reactive; Poisonous

Chlorine:

Dense; Green Gas; Fairly reactive; Poisonous

Bromine:

Red-brown volatile liquid; Dense; Poisonous

Iodine:

Dark grey crystalline solid OR purple vapour; Less reactive; Solid at room temperature; Poisonous

Noble Gases

Group 0 of Periodic Table (far-right)

Colourless; Inert; Non-metals; Monoatomic Gases

Have full outer shells

No need to lose/gain electrons to be stable (inert)

Trend as you go down Group 0:

Boiling point increases

Boiling point increases due to more electrons which leads to stronger intermolecular forces