OCR Chemistry Unit 1

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MODULE ONE

ATOMIC STRUCTURE

Protons, Neutrons and Electrons

Protons and neutrons make up nucleus and electrons orbit it.

Proton- Relative mass- 1.0, Relative charge- 1+

Neutron- Relative mass- 1.0 Relative charge- 0

Electron- Relative mass- 1/2000 Relative charge- 1-

Number of protons = number of electrons so it is electrically neutral.

Top number- Mass number Bottom number- Atomic number

DEFENITION- Mass number- is the number of protons and neutrons in the nucleus.

DEFEITION- Atomic number- is the number of protons in the nucleus of an atom.

Isotopes

DEFENITION- Isotopes are atoms of the same element with the same number of protons but different number of neutrons.

Isotopes have different mass because there is a different amount of neutrons.

Different isotopes of the same element react in the same way because reactions involve electrons, neutrons make no difference.

Atomic structure of ions

DEFENITION- An ion is a positively or negatively charged atom or group of atoms.

Lose/ gain electrons.

Ions are charged because they have different numbers of protons and electrons.

ATOMIC MASSES

Measurement of relative masses

We compare masses of different elements agaisnt the carbon- 12 isotope.

Relative isotopic mass

DEFENITION- is the mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12

Relative isotopic mass is the same number as the mass number (top number)

Relative atomic mass

DEFENITION- is the weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12

Example:

Sample of Bromine contains 53% of Br-79 and 47% of Br-81

Answer = 53/100 x 79 + 47/100 x 81= 79.94

Relative molecular mass

DEFENITION- is the weighted mean mass of a molecule compared with 1/12 of the mass of an atom of carbon-12

Can be found by adding together the relative atomic masses of each atom in a molecule. eg Cl2

Relative formula mass

DEFINITION- is the weighted mean mass of a formula unit compared with 1/12 of the mass of an atom of carbon-12

Can be found by adding together all relative atomic masses of each atom in a formula eg CaBr

ATOMS OF SUBSTANCE AND THE MOLE

Amount of substance

Amount of substance is given the unit, n

Amount of substance is based on a standard count of atoms called the Avogardo constant- is the number of atoms per mole of the carbon-12 isotope- 6.02 x 10 to the power of 23

DEFINITION- A mole is the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope.

Molar mass

DEFINITION- is the mass per mole of a substance.

Can be found by adding together all the realtive atomic masses for each atom the makes up a formula unit

Equations

N=  m/M

n= amount of substance

m= mass

M= molar mass

TYPES OF FORMULA

Empirical formula

DEFINITION- is the simplest whole number ratio of atoms of each element in a compound.

Example: Analysis showed that 0.6075g of…

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