Periodic table-History and Use

Who is Boyle

Irish chemist
Defined element

What is an element

Substance that cannot be split into simpler substances by chemical means.

What did davy do

Discovered potassium and sodium by electrolysis

Outline Mendeleev’s contribution to the periodic table

Periodic law- If elements are arranged in order of increasing atomic weight and elements with similar properties were placed beneath each other in groups, properties repeat at regular intervals.

How was Mendeleev able to predict the properties of elements like gallium and germanium before they were discovered?

Because elements in the same group have similar properties, Mendeleev realised the undiscovered element would have similar properties to other elements already in that group.

Why did Mendeleev place the tellurium before iodine in his periodic table even though it has a larger atomic weight?

Ensure elements with similar properties were in groups.

Outline Moseleys contribution to the periodic table

• Used x-rays to determine number of protons in nucleus of an elements atom
• Number of protons in the nucleus of an element is the atomic number
• Showed that if elements were arranged in order of increasing atomic number, elements with similar properties fall naturally into the same groups.

How does Mendeleev’s periodic table differ from the modern periodic table?

Mendeleev:

1. Arranged in order of increasing atomic weight

2. Contains gaps

3. Fewer elements

4. Transition elements not in separate block

Modern perioddic table:

1. Arranged in order of increasing atomic number

2. No gaps

3. More elements

4. Transition elements placed in seperate block

Relative charge, relative mass and location of proton

+1, 1 amu, Nucleus

Relative charge, relative mass, location of Neutron

0, 1 amu, nucleus

Relative charge, relative mass, location of electron

-1, 1/1840 amu, orbiting nucleus

What is an atom

Smallest part of element that retains the properties of that element

What is an ion

An atom with a charge

How does atom become ion

By gaining or losing electrons

What is negative ion called

Anion

What is positive ion called

Cation

Define atomic number

Number of protons in nucleus of an atom or ion

Define mass number

Total sum of protons and neutrons in nucleus

What are isotopes

Atoms of the same element that have the same atomic number but different mass numbers

How do different mass numbers arise? / Why do isotopes occur?

Different atoms can have different number of neutrons

Define relative atomic mass

Average mass of all isotopes in an element, taking abundances into account, relative to 1/12th of carbon 12 isotope.

Why are relative atomic masses rarely whole numbers

Average values

How are the relative atomic masses and relative molecular masses measured?

Mass spectometer

How to calculate relative atomic mass

(%no x mass no)/100 + (%no x mass no)/100

How many electrons can occupy an orbital

Two electrons is the max

Aufbau principle

Electrons must fill lowest available sub-levels first.

Why do electrons fill 4s sublevel before the 3d sublevel

4s sublevel is lower in energy than 3d sublevel.
According to Aufbau principle, electrons fill lowest available sub-levels first,

Hunds rule of maximum multiplicity

When two or more orbitals of equal energy are available electrons fill the orbitals singly before in pairs.

Pauli’s exclusion principle

Two electrons in an orbital must have opposite spin

Explain in terms of energy sublevels why the arrangement of electrons in the main energy levels in a calcium atom is 2, 8, 8, 2 and not 2, 8, 10

• Electrons fill lowest available sublevels first according to Aufbau principle
• 4s is lower in energy than 3d