Unit 2 - atoms, elements and compounds

A substance that can’t be broken down into anything simpler using a chemical reaction - only have 1 type of atom and each is unique

Formed when one or more atoms of different elements are joined together by chemical reactions

Formed when two or more substances are found together but not chemically bonded to each other - can be elements or compounds - can be easily separated

• Electrons • Neutrons • Protons

• Electrons - energy shells • Neutrons - in the nucleus • Protons - in the nucleus

• Radius of the nucleus is 10000x smaller than radius of the atom • Most of the mass is within the nucleus because protons and neutrons have the most mass

• Number of protons = proton/atomic number • Number of protons determines the element • Mass of 1 • Charge of +1

• Mass of 1 • Charge of 0 • Atoms of the same element but different amount of neutrons are isotopes

• Smallest sub-atomic particle • Mass of 1/2000 • Charge of -1 • Orbit the nucleus in shells • Number of electrons = number of protons - elements have no charge

• Nucleon/atomic mass number • Proton/atomic number

• Also known as proton number • Number of protons in an element • Shows amount of electrons in the element too

• Also known as nucleon number • Number of protons + number of neutrons

Atomic mass number - Proton number

The distribution of electrons of an atom or molecule in electron shells

• First shell = Max of 2 • Second shell = Max of 8 • Third shell = Max of 8 • Fourth shell = Max of 18 • …

• Written in the form x,x,x, • Example - Aluminum = 2,8,3

Noble gases - Group VIII

Charged atoms

• Obtain a full outer shell through losing or gaining electrons

• Group 1 = 1+ • Group 2 = 2+ • Group 3 = 3+ • Group 4 = 4+- • Group 5 = 3- • Group 6 = 2- • Group 7 = 1- • Group 8 = 0

Atoms with the same number of protons but different numbers of neutrons

• Mass number on upper-left • Atomic number on lower-left • Chemical symbol on the right • If ion, charge is on upper-right of chemical symbol

• Average Atomic mass = Sum of [(Atomic mass x % abundance)] for each isotope ÷ 100 • Average Atomic mass = sum of [(atomic mass x relative abundance)] for each isotope ÷ sum of the relative abundance

Occurs between metal and non-metal atoms - metal donates electrons to the non-metal for both to obtain full shells