WJEC A Level Chemistry Unit 1

oxidation number of an uncombined element

0

oxidation number of group 1 metals

+1

oxidation number of group 2 metals

+2

oxidation number of oxygen

-2 (EXCEPT: +2 with fluorine and -1 in peroxides)

oxidation number of hydrogen

+1 (EXCEPT: -1 in metal hydrides)

what do ionic equations show

only the particles that react and the products they form, ions that do not change are LEFT OUT

atomic number

number of protons

mass number

sum of protons and neutrons

isotope

same atomic number different mass number - same protons different neutrons

radioactive decay

an unstable atomic nuclei loses energy by radiation or particle to become stable

what are alpha particles

positively charged helium nuclei

what is the charge of alpha particles

+2 charge

what is the relative mass of alpha particles

4

what can stop alpha particles

paper/Skin

what is the ionising power of alpha particles

high

what is the penetrating power of alpha particles

low

how do alpha particles behave in an electric field

deflect towards negative electric field - heavy, slow moving

how do alpha particles behave in a magnetic field

low deflection - attracted slightly

what are beta particles

high speed negatively charged electrons

what is the charge of beta particles

-1

what is the relative mass of beta particles

0

what can stop beta particles

Thin metals (aluminium)

what is the ionising power of beta particles

medium

what is the penetrating power of beta particles

medium

how does a beta particle behave in an electric field

deflect towards positive - light and fast

how does a beta particle behave in a magnetic field

high deflection - considerable deviation

what is gamma radiation

very high energy electromagnetic radiation

what is the charge of gamma radiation

none

what is the relative mass of gamma radiation

negligible

what can stop gamma radiation

lead

what is the ionising power of gamma radiation

low

what is the penetrating power of gamma radiation

high

how does gamma radiation behave in an electric field

undeflected

how does gamma radiation behave in a magnetic field

no deflection

alpha decay

mass number -4

atomic number -2

beta decay

atomic number +1

electron capture

mass number -1

positron emission

mass number -1

half life

the time taken atoms/mass in a radioactive substance to half

what is half life NOT affected by

catalysts and changes in temperature

what effect does radiation have on DNA in living cells

it damages DNA, which can cause mutations, and cell death at higher doses

what can mutations in cells lead to

formation of cancerous cells

what can high levels of radiation exposure cause

radiation burns and death

beneficial uses of radioactivity

-cancer treatment (radiotherapy)

-calculating age of plant and animal remains

-estimating geological age of rocks

-production of electricity

what is the shape of an S orbital and how many electrons can it hold

spherical and 2

what is the shape of a P orbital and how many electrons can it hold

dumbbell and 6

what is ionisation energy

the energy required to remove an electron from an atom

why do successive ionisation energies increase

greater effective nuclear charge

-as each electron is removed each shell is drawn slightly closer to the nucleus, therefore increased nuclear attraction needing more energy to break.

equation for frequency

c = f λ

(c = speed of light)

(f = frequency)

(λ = wavelength)

what happens if atoms are given energy (via heating or electrical field)

electrons get excited and are promoted from a lower energy level to a higher energy level - when the source of energy is removed the electrons fall from their higher energy level and from their excited state to a lower energy level and energy is released as a photon (quantum of energy)

equation for energy

e = h f

(e = energy)

(h = plank's constant)

(f = frequency)

FREQUENCY IS PROPORTIONAL TO ENERGY AND WAVELENGTH IS INVERSELY PROPORTIONAL TO ENERGY

balmer series

visible region, electrons return to n = 2

lyman series

ultraviolet, electrons return to n = 1

relative atomic mass

average mass of one atom of the element relative to 1/12 the mass of a carbon-12 atom

relative isotopic mass

mass of one atom of an isotope relative to 1/12 the mass of a carbon-12 atom

relative formula mass (M r)

the total average mass of all the atoms in the formula relative to 1/12 the mass of a carbon-12 atom

what can be used to find the relative atomic mass of an element

a mass spectrometer

what does a mass spectrometer measure

the relative mass of each different isotope of an element

the relative abundance of each isotope of the element

what does a mass spectrometer look like

why is a vacuum used inside

it's important that air molecules do not interfere with the movement of the ions

stages of mass spectrometry

vaporisation, ionisation, acceleration, deflection, detection

ionisation in a mass spectrometer

vapourised sample passes into the ionisation chamber and the sample particles are bombarded with a stream of electrons, some of the collisions knocking an electron out of the particles to make positive ions

acceleration in a mass spectrometer

the positive ions are accelerated to a high speed by an electric field

deflection in a mass spectrometer

ions are deflected by magnetic field, the lighter ones being deflected more than the heavier ones and ions with 2 positive charges are deflected more than those with 1 - THESE 2 FACTORS ARE COMBINED IN THE M/Z RATIO (MASS/CHARGE)

detection in a mass spectrometer

only ions with a given M/Z ratio make it to the ion detector - electrons are transferred from detector plate to positive ion which creates a current

the larger the current, the higher abundance of the isotope

determining relative atomic mass of an element (A r)

(if on a graph with the lines, X axis x Y axis over 100 for A r

what is a mole

the amount of a substance in grams that contains as many particles as there are atoms in 12 g of carbon-12

1 mol = 6.02x10'23 (avogadros constant!)

what is molar mass

the mass of one mole of a substance

moles equation

moles = mass/Mr

atom economy equation

percentage yield = (mass of product obtained ÷ maximum theoretical mass) X 100

ionic bonding

when a metal and non-metal react together, the metal atom loses electrons and becomes a cation (+) and the non-metal gains electrons and becomes an anion (-)

strong electrostatic forces of attraction between these

dot cross diagrams (steals electrons)

covalent bonding

when non metals bond together, each atom gives one electron to form a bond pair in which the electron spins are opposed - the bond is the electrostatic attraction between positive nuclei of bonded atoms and shared electrons between them

dot cross diagrams (electrons shared, overlaps)

coordinate bonding

a covalent bond where both electrons come from one atom

what is electronegativity

a measure of how strongly atoms attract electrons in a covalent bond

-the higher the electronegativity value, the better the element can attract bonding electrons

-Strongest at top right of Periodic table (Li)

polar bonds

one atom slightly negative, one atom slightly positive

bonding between molecules

intermolecular

bonding within molecules

intramolecular

intermolecular bonding

weak, governs physical properties (eg. boiling temp)

intramolecular bonding

strong, governs chemical reactivity

dipole

a molecule that contains both positively and negatively equal charges

Atom

The smallest part of an element that can exist. All substances are made up of atoms.

Compound

A substance that combines two or more different elements through the formation of chemical bonds.

Ion

Formed when an atom/molecule loses or gains electrons. This gives it an overall charge - a positive charge if it has lost at least one electron and a negative charge if it has gained at least one electron.

Ionic equation

A chemical equation that involves dissociated ions.

Molecular formula

The actual number of atoms of each element in a molecule.

Oxidation number

The charge of an ion or a theoretical charge of an atom in a covalently bonded compound assuming the bond becomes ionic.

State symbol

Symbols which show the physical state of the substance during the reaction, they are usually in brackets: gas (g), liquid(l), solid(s) and aqueous(aq). Aqueous means the substance is dissolved in water.

Absorption spectra

A spectrum of frequencies of electromagnetic radiation that has been transmitted through an atom or molecule, that shows dark bands due to the absorption of the radiation at those specific wavelengths.

Alpha-decay

A type of radioactive decay, during which an atomic nucleus loses two protons and two neutrons. An alpha particle is equivalent to a helium nucleus. It reduces the atomic number by two and the mass number by four, making the element more stable.

Atomic number

Total number of all the protons in the nucleus. It increases as you go across the periodic table.

Beta-decay (positron emission)

A type of radioactive decay, during which a beta particle is lost, which is equivalent to an electron and a neutron turns into a proton or a proton turns into a neutron. This changes the atomic number by one, but the mass number remains the same.

d orbitals

Regions in which up to two electrons can be found. There are five d orbitals, so in total, the d subshell can hold up to 10 electrons.

Electromagnetic spectrum

The range of frequencies of electromagnetic radiation and the respective wavelengths.

Electron capture

Occurs to make an atom more stable, an electron from the atom's inner shell of electrons moves into the nucleus where it joins with a proton, this forms a neutron and a neutrino. The neutrino formed is expelled from the atom's nucleus.

Electron configuration

The arrangement of electrons into orbitals and energy levels around the nucleus of an atom/ion. E.g. Ca: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².

Electron transition

When an electron absorbs energy and moves from a low energy orbital to a vacant higher energy orbital.

Emission spectra

A spectrum of frequencies of electromagnetic radiation that has been emitted by an atom or molecule undergoing a transition from a state with higher energy to a state with lower energy.

Energy level

The shell that an electron is in.

First ionisation energy

The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1⁺ ions. For example, Mg(g) → Mg⁺(g) + e⁻.

Frequency

The number of wave oscillations per second.