Chemistry topic 1 Elements of life

Explain the model of Dalton’s Billiard Balls Model

• All matter is made of indivisible particles called atoms

• All atoms of the same element are identical to each other

• Did not include any idea of sub-atomic particles

Explain Thomson’s Plum Pudding Model

• The atom is a spherical cloud of positive charge with small negatively charged particles embedded within.

• Atoms are overall neutral due to the charge of electrons cancelling out with the positive charge so an atom is neutral.

• DOESN’T INCLUDE IDEAS ABOUT PROTONS.

Explain Rutherford’s Planetary model.

• Introduced the nucleus.

• Atoms are mostly made up of empty space.

• At the centre there is a small, dense, positively charged nucleus containing most of the mass.

• Negatively charged electrons orbit the nucleus.

Explain the evidence and experiment behind Rutherford’s Planetary model.

• Fired a beam of alpha particles at a thin sheet of gold foil.

• Most of the alpha particles passed through.

• Some were strongly deflected and could even bounce right back.

• The deflected alpha particles were on a collision course with a small, heavy, positively charged nucleus.

• The undeflected alpha particles passed through empty space around the nucleus.

Explain Bohr’s Quantum Model.

• A dense positively charged nucleus with empty space.

• Electrons found around the nucleus.

• Electrons are restricted to certain number energy levels.

• Energy and number of electrons that can be held increases as you get further away from the nucleus.

Explain the evidence and experiment of Bohr’s Quantum Model.

Emission Spectra

• When an element is strongly heated it emits light.

• Certain specific frequencies of light are emitted,

• Heating causes electrons to be excited to higher energy levels.

• As electrons drop down, the energy that they absorbed is emitted in the form of light.

• Each possible drop releases a certain amount of energy.

Ionisation Enthalpies

• Amount of energy needed to remove electrons from an atom is called ionisation enthalpies.

• Some electrons require much less energy to remove that others.

• Must be electrons in the outer shell which are attracted much less strongly to the nucleus than inner electrons.

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What is an isotope?

Atoms with the same atomic number but different mass number.

How is the relative isotopic mass of an atom defined?

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

How is the relative atomic mass defined?

The average mass of all atoms in a sample of an element compared to one twelfth of the mass of a carbon-12 atom.

What is a mass spectrometer used for?

To find out the number of isotopes an element has, the mass of each of them and the relative abundance of each isotope.

What does nuclear fusion involve?

The nuclei of two ( or more ) colliding and fusing to make one ( or more ) heavier nuclei.

What are the requirements for nuclear fusion to occur and why?

High temperatures and pressures because a lot of energy is needed to overcome the repulsion between two positively charged nuclei.

What are electron shells made up of?

Sub-shells ( s, p and d sub-shells )

What sub-shells are contained in each electron shell?

Electron shell 1- s sub-shells only

Electron shell 2- s and p sub-shells

Electron shell 3- s, p and d sub-shells

Electron shell 4- s, p, d and f sub-shells

What is an orbitial?

A region of space that can hold up to 2 electrons

( each of the electrons has the same energy, but will have an opposite spin )

How many orbitals is each sub-shell made up of and how many electrons can be held ?

• s sub-shells are made up of one orbital so can hold 2 electrons in total.

• p sub-shells are made up of three orbitals so can hold up to 6 electrons in total.

• d sub-shells are made up of five orbitals so can hold up to 10 electrons in total.

• f sub-shells are made up of seven orbitals so can hold up to 14 electrons.

Explain the shapes of the s and p sub-shells.

• s sub-shells are spherical in shape.

• p sub-shells have a dumbbell shape and each sub shell has three orbitals that lie in different orientations ( aligned along perpendicular axes ).

What is the order in which the electrons fill in the sub-shells?

1s 2s 2p 3s 3p 4s 3d 4p

What are the two exceptions to the rule that the 4s sub-shell is completely filled before the 3d sub-shell?

chromium and copper