Chemistry

Atomic mass:

  • protons and neutrons are similar, each around 1 atomic mass unit

  • electrons barely have any mass, generally neglected when calculating atomic mass

  • 1 electron ~= 1/1800 x 1 proton’s mass

Element symbol:

  • consists of 1 - 2 letters

  • first letter always capitalised, second lower case

  • usually from the Latin name of the element

Bohr model:

  • only works well for first 18 elements

  • model shows: - proton#, electron#, neutron#, nucleus, electron shells

  • 2, 8, 8 electrons in the 1st, 2nd, 3rd energy levels respectively

Atoms in general:

(main) Subatomic particles:

  • Protons: +, found in nucleus

  • Neutrons: o, found in nucleus

  • Electrons: -, found in orbitals

  • electrons are 1800 times smaller than a proton

Energy levels (extends into Schrödinger’s model):

  • there are many energy levels - 1, 2, 3, 4…

  • each energy level has a certain amount of subshells - s, p, d, f, g, h…

  • each subshell has a certain amount of orbitals

  • each orbital can hold 2 electrons

  • s can hold 1 orbital

  • p can hold 3 orbitals

  • d can hold 5 orbitals

  • f can hold 7 orbitals

the first energy level has one subshell, then as the energy level increases, each has one more subshell. 1s, 2s, 2p, 3s, 3p, etc…

  • electrons occupy the ‘shell’ with the lowest energy level available first

  • the order is expressed by the diagrams on the left

  • can be listed below:

  • 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s…

  • Schrödinger found that electrons do not have specific, set ‘shells’

  • instead, he drew orbitals for them — an orbital is where an electron has a high possibility of being found in

  • each ‘shell’ thus holds a maximum of 2(n^2) electrons, where n is the shell number

Different atoms of the same element:

  • same proton #, same neutron #, same electron #

  • different proton #

  • same proton #, same neutron #, diff. electron #

  • same proton #, diff. neutron #, same electron #

→ regular atom

→ different elements

→ ions

→ isotopes

ions have either lost or gained electrons.

  • negatively charged ions → anions (think: onion = 😢)

  • positively charged ions → cations (think: cats = 😺)

Reactivity:

  • an atom is reactive when it doesn’t have a complete outermost shell of 8 valence electrons

  • the octet rule states that 8 valence electrons is a relatively stable configuration

  • the reactivity of an atoms depends on how easily it could gain/lose electrons to achieve a complete outer shell

Factors of reactivity:

(how easy it is to lose/gain electrons to achieve 8 valence electrons)

  • no. of valence electrons

    • atoms with 1 and 7 valence electrons are most reactive

    • atoms with 4 and 8 valence electrons are relatively stable

  • electronegativity

    • electronegativity is the tendency of an atom to attract electrons towards itself

    • →→ attraction between electrons and protons of an atom

    • weaker electronegativity makes atoms forming cations more reactive because it’s easier to lose electrons

    • stronger electronegativity makes atoms forming anions more reactive because it’s easier to gain electrons

  • atomic radius

    • atomic radius is the radius of an atom

    • atomic radius affects electronegativity

  • core charge

    • the net charge of the nucleus

    • increases with proton #, neutrons have neutral charge so does not affect it

    • increases accross a period (more protons)

    • affects electronegativity & atomic radius → electrons more attracted

  • energy levels

    • increases down a group

    • electron energy increases with energy level

    • electrons with higher energy wander further away from the nucleus

    • affects electronegativity & atomic radius → electrons have higher energy thus wander away, less attracted

  • if an element in a compound is usually able to form more than one ion, usually transition metals, then a roman numeral is added in brackets after its name to indicate its charge

  • copper (III) means copper with 3 gained electrons

Forming ions:

← Lewis dot diagram for the reaction between magnesium and chlorine, become magnesium chloride.

  • A binary ionic compound is formed by a metal and a non-metal, which forms a cation and an anion respectively

  • to name a binary inoic compound, the metal is named first, and the end of the non-metal’s name is replaced by -ide

  • lithium chloride, aluminium oxide, copper (II) sulfide, etc.

When naming ions, the positive ion is always placed first.

The ions’ charges combine to form zero.

Subscripts are used to convey amount of an ion. If the ion is polyatomic, then brackets are also used.