4.1 - Atomic Structure and the Periodic Table

Define atom

The smallest part of an element that can exist

Define element

A substance made up of 1 type of atom

Define compound

• Compounds contain two or more elements chemically combined in fixed proportions.

• Can be represented by formulae using the symbols of the atoms from which they were formed.

• Compounds can only be separated into elements by chemical reactions.

Define mixture

• A mixture consists of two or more elements or compounds not chemically combined together.

• The chemical properties of each substance in the mixture are unchanged.

• Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography.

• These physical processes do not involve chemical reactions and no new substances are made.

Roughly how many elements are there

There are about 100 different elements.

Define isotope

Variations of an element, with the same number of protons and electrons, but different numbers of neutrons

Define molecule

Two or more non-metals, covalently bonded

How do you calculate the A_r (relative atomic mass) of a substance

((Percentage of isotope 1 x mass 1) + (Percentage of isotope 2 x mass 2)…)/100= A_r

Describe filtration

Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper.

Apparatus: filter paper + funnel.

Describe distillation

• Simple distillation is used to separate liquid from a solution – the liquid boils off and condenses in the condenser.

• The thermometer will read the boiling point of the pure liquid.

• Contrary to crystallisation, we get to keep the liquid.

Describe crystallisation

• Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent (e.g. salt from H2O).

• The solution is heated until all the solvent evaporates; the solids stays in the vessel.

• Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved).

• Then, we cool down the solution.

• As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures.

• The crystals can be collected and separated from the solvent via filtration.

Describe chromatography

• Chromatography is used to separate a mixture of substances dissolved in a solvent.

• In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent.

• The bottom of the paper has to be in contact with the solvent.

• The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).

Describe what fractional distillation separates

• Fractional distillation is a technique for separation of a mixture of liquids.

• It works when liquids have different boiling points.

• The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.

• The fractionating column contains glass beads. It helps to separate the compounds.

• In industry, mixtures are repeatedly condensed and vapourised.

• The column is hot at the bottom and cold at the top.

• The liquids will condense at different heights of the column

What is a seperating funnel

A separatory funnel is an apparatus for separating immiscible liquids. Two immiscible liquids of different densities will form two distinct layers in the separatory funnel. We can run off the bottom layer (the liquid with greater density) to a separate vessel.

What is the diameter of an atom

1×10^-10m

What is the diameter of the nucleus

1×10^-14

What are the charges of protons, neutrons, and electrons?

proton-1+
neutron-0
electron-1-

What are the relative masses of protons, neutrons, and electrons?

proton-1
neutron-1
electron-0 (0.0005)

Describe the process of the development of the atom

1803- John Dalton- Hard Ball- Atoms

1903- JJ Thompson- Plum Pudding Model- Electrons

1911- Ernest Rutherford- Nuclear Model (Alpha Particle Scattering experiment)- Positive Nucleus

1913- Niels Bohr- Bohr's Model- Electron Shells

1934- Chadwick- Quantum model- Neutrons

What was the first model of the atom

Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.

Describe the plum pudding model

• The discovery of the electron led to the plum pudding model of the atom.

• The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.

• The mass is evenly distributed

Describe the alpha particle scattering experiment, and what it concluded

• Rutherford fired alpha particles, which have a charge of 2+, at a sheet of thin gold foil

• Some were reflected, as they hit the gold nucleus, and some were deflected, as they were repelled by the positive charge of the nucleus- this proved the positive charge was concentrated in the nucleus

• Most just passed straight through- this proved the atom was mostly empty space

• His model, the nuclear model had the mass and positive charge concentrated in the central nucleus, with one layer of electrons orbiting outside- most of the atom was empty space

How did bohr’s model differ from the nuclear model

Bohr’s model had shells of electrons with increasing energy levels as they get further from the nucleus. When atoms absorb energy, they can move up energy level(s), and when they emit energy, in the form of an electromagnetic wave, they can move back down an energy level

How did Mendeleev organize his periodic table?

In order of increasing atomic weight

What did Mendeleev do to make the groups' trends work

• He swapped elements which didn’t fit the pattern of increasing atomic weight so that groups had similar trends

• He left spaces for undiscovered elements, which he could predict the qualities of through its period and group. When these elements, such as gallium, were discovered, and matched his predictions, Mendeleev’s periodic table gained validity.

Which group wasn't on Mendeleev's table and why

Group 0- They are very unnreactive (inert) so were hard to detect, and had not been discovered yet

Why couldn't Mendeleev order his table the way we do

We do it by atomic number (number of protons), but protons hadn't been discovered as it was 1869, so they were still on the hard ball model

Describe the features of group 1

• Alkali Metals

• Extremely reactive, especially with group 7

• Form 1+ ions

• Relatively low density (for a metal)

• Soft and Dull

• Form hydroxides (alkaline solutions) when dissolved in water

• 1 electron in the outer shell

• Reactivity increases down the group

• Boiling point decreases down the group

Describe the features of group 7

• Halogens

• Extremely reactive

• Form 1- ions

• Form diatomic molecules

• Some gases, some liquid, some solid

• Often examples in displacement reactions

• 7 electrons in the outer shell/ 1 less than a full outer shell

• Reactivity decreases down the group

• Boiling point increases down the group

Describe the features of group 0

• Noble gases

• Extremely unnreactive (innert)

• Do not form ions as they are stable

• Exist in their native state

• All gases

• Can be used in double glazing (windows), welding, balloons (He), lights and signs (Ne)

• Full outer shell- stable

• Reactivity increases down the group (slightly)

• Boiling point increases down the group

Explain the trend in reactivity for group 1 and group 7

In group 1, as you move down the group, there are more shells, so there is more electron shielding; this means that the outer electron has less electrostatic attraction between the positive nucleus and the negative outer electron. As a result, it is easier for the atom to transfer its outer electron to another atom and react; this means as you go down group 1, it is easier for the metal to transfer its outer electron, and reactivity increases

As you go down group 7, there are more shells, and therefore more electron shielding; this means there is less electrostatic attraction between the negative outer shell and the positive nucleus. As a result, it is harder for the outer shell to attract the last electron needed, so it is harder for it to react; this means that as you go down group 7, it is harder to attract the last electron to form a full outer shell, so reactivity decreases.

Draw a lithium ion

[2]⁺

Draw a fluoride ion

[2,8]^-

Describe the physical and chemical properties of transition metals

Chemical Properties

1. They can form multiple different ions, like Fe²⁺ and Fe³⁺

2. Their ions form different coloured solutions and compounds

3. They are used as catalysts

Physical Properties

1. Dense, malleable, ductile

2. Sonorous

3. Good conductors of electricity and heat

4. High melting and boiling points