2.1.1 Atomic Structure and Isotopes & 2.1.2 Compounds, Formulae and Equations

Dalton's atomic theory

Atoms are tiny particles made of elements; Atoms cannot be divided; All the atoms in an element are the same; Atoms of one element are different to those of other elements.

Thompson's discovery about electrons

They have a negative charge; They can be deflected by magnet and electric field; They have very small mass.

Plum pudding model

Atoms are made up of negative electrons moving around in a sea of positive charge.

Rutherford's proposal after the gold leaf experiment

Most of the mass and positive charge of the atom are in the nucleus; Electrons orbit the nucleus; Most of atom's volume is the space between the nucleus and the electrons; Overall positive and negative charges must balance.

Current model of the atom

Protons and neutrons are found in the nucleus; Electrons orbit in shells; Nucleus is tiny compared to the total volume of atom; Most of atom's mass is in the nucleus; Most of the atom is empty space between the nucleus and the electrons.

Charge of a proton

1+.

Charge of an electron

1-.

Particle with the same mass as proton

Neutron.

Particles that make up most of atom's mass

Protons and neutrons.

Letter representing atomic number

Z.

What atomic number tells about an element

Atomic number = number of protons in an atom.

Letter representing mass number

A.

How mass number is calculated

Mass number = number of protons + number of neutrons.

How to calculate the number of neutrons

Number of neutrons = mass number - atomic number.

Isotope

Atoms of the same element with different number of neutrons.

Why different isotopes of the same element react in the same way

Neutrons have no impact on the chemical reactivity; Reactions involve electrons, isotopes have the same number of electrons in the same arrangement.

Ions

Charged particles that are formed when an atom loses or gains electrons.

Charge of the ion when electrons are gained

Negative.

Unit used to measure atomic masses

Atomic mass unit (amu).

Positive charge

When electrons are lost

3+ ion

Has lost 3 electrons

Unit used to measure atomic masses

Unified atomic mass unit, u

Relative atomic mass

The weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon-12

Unit of relative atomic mass

No units

Relative isotopic mass

The mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12

Relative isotopic mass equivalence

Same as mass number

Assumptions when calculating mass number

1. Contribution of the electron is neglected 2. Mass of both proton and neutron is taken as 1.0 u

Relative molecular mass and relative formula mass calculation

Both can be calculated by adding the relative atomic masses of each of the atom making up the molecule or the formula

Uses of mass spectrometry

●Identify unknown compounds ●Find relative abundance of each isotope of an element ●Determine structural information

How a mass spectrometer works

●The sample is made into positive ions. ●They pass through the apparatus and are separated according to mass to charge ratio. ●A computer analyses the data and produces mass spectrum.

Group number relation to electrons

Group number = number of electrons in the outer shell

Group number in the periodic table

Indicates vertical column

Metals and electrons

Metals usually lose electrons

Elements that don't form ions

Beryllium, boron, carbon, and silicon; requires a lot of energy to transfer outer shell electrons

Molecular ions

Covalently bonded atoms that lose or gain electrons

Charge of ammonium ion

+1 → NH4+

Charge of hydroxide ion

-1 → OH-

Charge of nitrate ion

-1 → NO3-

Charge of carbonate ion

-2 → CO3 2-

Charge of sulfate ion

-2 → SO4 2-

Empirical formula

Simplest whole number ratio of atoms of each element present in a compound

Calculating empirical formula

●Divide the amount of each element by its molar mass ●Divide the answers by the smallest value obtained ●If there is a decimal, divide by a suitable number to make it into a whole number