2 Atoms, ions and compounds

def relative isotopic mass

the mass of an isotope relative to 1/12th of the mass of an atom of carbon-12.

Relative isotopic mass has no units because it’s a ratio of 2 masses.

def relative atomic mass (Ar)

(most elements contain a mixture of isotopes, each with a different isotopic mass) relative atomic mass (Ar) is the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12.

def relative molecular mass (Mr)

the mass of a single molecule on a scale on which the mass of an atom of carbon-12 has a mass of 12 atomic mass units

how is Mr calculated

by adding together the relative atomic mass (Ar) of the atoms in the chemical formula

def isotopes

atoms of the same element with different numbers of neutrons and different masses

what is the mass of an electron

negligible mass, about 1/1850

def atom

the smallest, electrically neutral particle of an element that can take part in a chemical change

def molecule

the smallest, electrically neutral, particle of an element or compound that can exist on its own

def ion

an atom, or group of atoms, which carries an electric charge

name the diatomic elements

Iodine

Hydrogen

Nitrogen

Bromine

Oxygen

Chlorine

Fluorine

what do groups show on the periodic table

the number of electrons in the outer shell

what do periods show on the periodic table

the number of shells

(Ar) how are the percentage abundances of isotopes in a sample of an element typically found

using a mass spectrometer

describe how a mass spectrometer works

1. a sample is placed in the mass spectrometer

2. the sample is vaporised and then ionised to form positive ions

3. the ions are accelerated. Heavier ions move more slowly and are more difficult to deflect than lighter ions, so the ions of each isotope are separated.

4. the ions are detected on a mass spectrum as a mass-to-charge ratio (m/z). Each ion reaching the detector adds to the signal, so the greater the abundance, the larger the signal.

what are mass spectra produced by

mass spectrometers

what does mass spectra show us

the relative isotopic masses of different elements

and

the abundances of different elements

what can mass spectra be used to work out

the relative atomic masses of different elements

Ar = the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12

how can you calculate the relative atomic mass (Ar) of a sample using a m/z graph

1. multiply each relative isotopic mass by its relative isotopic abundance, and add up the results

2. divide by the sum of the isotopic abundances

what is the avogadro constant

6.022 x10^23 of something

how can you calculate the number of molecules of something when given the mass and compound formula?

calculate the moles

x the moles by the avogadro constant (6.022 x10^23)

how do you get mmol to mol

/1000

how do you get cm^3 to dm^3

/1000

how do you find out the limiting reagent of an equation?

calculate the moles of all reactants then compare how much each reactant needs of the other reactant (ratio)

how do you write an ionic equation

1. write down the full formula (including state symbols)

2. identify which compound/element stays in the same state from start to finish - that is the spectator ion. ignore the spectator ion

3. write down the NON- spectator ions with their charges and state symbols

4. balance element to element

atomic number

the number of protons in the nucleus of an atom

electron

a negatively charged subatomic particle

orbits the nucleus at various energy levels

relative mass is 1/1836

ion

a charged atom or molecule

isotopes

atoms of the same element w the same no. of protons and e- but diff numbers of neutrons

isotopes of an element have diff masses

mass no.

total no. of protons and neutrons in nucleus of atom

mass spectrometry

an instrument which gives accurate info about relative isotopic mass and relative abundance of isotopes

neutron

neutral subatomic particle found in nucleus of atom

relative mass is 1

proton

positively charged subatomic particle found in nucleus of atom

relative mass is 1

relative abundance

amount of one substance compared w another

relative atomic mass

the mass of an atom of an isotope compared w 1/12th mass of an atom of carbon-12

relative formula mass

mass of the formula unit of a compound w a giant structure

e.g. NaCl has a relative formula mass of 58.44gmol-1

relative molecular mass (Mr)

mass of a simple molecule

relative atomic mass =

Σ (%abundance x mass)/100

what r the stages of mass spectroscopy

1. ionisation (e- gun knocks 1e- off)

2. acceleration of ions (all ions same speed)

3. drift zone (speed measured)

4. detection

how does mass spectroscopy work

• atom/molecules are ionised to form 1+ ions

• ions are accelerated in an electric field so they all have the same kinetic energy

• ion drift: ions enter flight tube

• ions with diff masses have a diff time of flight

• lighter ions travel faster so take less time to reach detector

• detector is a negatively charged plate, current produced when ions hit plate, more ions hitting detector the bigger the current

what is Avogadro constant

6.022 ×10²³ of something

number of particles in each mole of carbon-12

how do u calculate the no. of molecules of something

moles x 6.022 ×10²³