Atoms, Elements and Compounds

Atomic Structure and the Periodic Table

Proton number: number of protons in an atom (and number of electrons in an atom)

Nucleon number: number of protons + neutrons in an atom.

Isotopes: atoms of same element with different no. of neutrons

E.g. Carbon 12 and Carbon 14.
Two types: non-radioactive isotopes and radioactive-isotopes which are unstable atoms that break down giving radiations
Medical use: cancer treatment (radiotherapy) -- rays kill cancer cells using cobalt-60
Industrial use: to check for leaks -- radioisotopes (tracers) added to oil/gas. At leaks radiation is detected using a Geiger counter.

In the periodic table

The proton number increases by 1 when you go to the right
When you go one element down, you increase proton number by 8 in the first 3 periods (transition elements not included)

Electrons are arranged in electron shells.

Atoms want to have full outer shells (full set of valency electrons), this is why they react.

Noble gases have full outer shells so they have no need to react.

Electron shell structure: 2, 8, 8, 18.

More reactive elements have a greater desire to have a full outer shell, so also form more stable compounds.

Element: substance that cannot be split into anything simpler, in a chemical reaction. Each element has a unique proton number.

Mixture: two or more elements mixed together but not chemically combined

Compound: substance in which two or more different elements are chemically combined

Metals	Non-metals
Strong	Brittle
Good conductors of heat & electricity	Poor conductors of heat & electricity (except graphite)
High m.p. and b.p.	Lower m.p. and b.p. than metals
High density	Low density
Forms basic oxides	Forms acidic oxides
Forms cations in reactions	Forms anions in reactions
Malleable and ductile
Sonorous
Some are magnetic

Alloy: Mixture of two or more metals or mixture of one or more metal with a non-metal, to improve its properties

Chemical bond formed by transfer of s from one atom to another

Metals lose s to form cations, non-metals gain s to form anions

Positive cations & negative anions attract to each other

Strong electrostatic force of attraction between positive cations and negative anions is called ionic bonding

Property	Reason
Form giant lattice	Cations and anions attract
High m.p. and b.p.	Strong bonds between ions
Don't conduct electricity when solid	Ions can't move
Conduct electricity when molten/aqueous	Ions can move
Usually soluble in water	Not required

When atoms share s to obtain a noble gas electron structure.

Covalent bonding takes place between non-metals only.

Single Bond	Double Bond	Triple Bond

2ē shared	4ēs shared	6ēs shared

Property	Reason
Low m.p. and b.p.	Weak intermolecular forces of attraction between molecules
Usually liquid, gas or low m.p solid	No mobile ions/electrons
Don't conduct electricity	Not required
Usually insoluble in water

Example:

Diamond	Graphite	Silicon Dioxide

Four bonds	Three bonds	Makes up sand
High m.p.	Made of flat sheets	Each Si is bonded to 4 oxygen atoms, and each oxygen is bonded to 2 silicon atoms
Doesn't conduct	Held together by weak forces so is soft ∴ used as a lubricant	∴ it has a high m.p. and is hard, like diamond
Used for cutting as is srongest known substance	Conducts electricity as it has one free e-