Chemistry: C1 & C2 Atomic Structure and the Periodic Table

History of the Atom

Scientist/person

What did they discover?

Ancient Greeks

Gave the first idea of tiny particles - atoms

John Dalton

Atomic theory

J.J. Thompson

Electrons, plum pudding model

Ernest Rutherford

Largely empty space - nucleus

Niels Bohr

Came up of the idea of shells

Chadwick

Neutron

Plum Pudding Model

  • Ball of positive charge with the electrons scattered across the ball. Alpha particles would pass through.

Nuclear Model

  • Mass in centre (nucleus)

  • Positive nucleus in centre

  • Alpha particles hit nucleus and bounce off

  • Most of atom is empty space

Charge

  • Electron - negative

  • Proton - positive

  • Neutron - neutral

Mass

  • Electron - 1/2000

  • Proton - 1

  • Neutron - 1

Isotopes

  • Isotopes are atom of the same element with the same number of protons and electrons but different number of neutrons

  • (mass no. X percentage) + ( 2nd mass X 2nd percentage ) / 100

Drawing atoms

  • 1st shell - up to 2 electrons

  • 2nd shell - up to 8 electrons

  • 3rd shell - up to 8 electrons

  • 4th shell - up to 14 electrons

  • The group number tells you how many electrons in the outer shell

Ions

  • Overall, atoms have a neutral charge because same number of electrons and protons

  • Full outer shell

  • Brackets

  • Correct charge

Constructing Formulae

  • The charge of both elements must be equal

Distillation

Simple distillation

  • Separate out a liquid from a solution

  • flask, bung, solution, thermometer, condenser, beaker, Bunsen burner

  • Heat mixture, pressure forces it down condenser, vapor cools in water jacket and condensates which runs down the pipe into the beaker

Fractional distillation

  • Separating mixture of liquids

  • similar to simple, but with a fractionating column - glass rods from bottom to top

  • heat to lowest boiling point, repeat to for other substances

Separating Mixtures

  • Element - substance made of 1 type of atom

  • Compound - a substance made of 2 or more different types of element chemically bonded

  • Mixture - a substance made of 2 or more different elements or compound not chemically bonded - easy to separate

  • Insoluble - doesn’t dissolve

  • Filtration - a method for separating an insoluble solid from a liquid

  • Chromatography - it works because some of the coloured substances dissolve in the solvent used better than others, so they travel further up the paper

  • Crystallisation - solution is heated so that the water evaporates away leaving solid crystals behind

  • distance of colour / distance of solvent

Development of the periodic table

  • John Dalton arranged them based on the atomic weight

  • John Newland built on the idea and noticed that every 8th element seemed similar when arranged by mass. Octaves only worked up to Calcium

  • Russian chemist, Dmitri Mendeleev, arranged element so a periodic pattern could be seen. Left gaps meant undiscovered elements was able to be predicted.

  • Not all elements fit in - argon has a greater relative mass then Potassium

  • In 20th century, they ordered by protons

Chemical equations

  • Chemical reactants and products - word equation

  • No atoms are created or destroyed during a symbol equation

  • You can add state symbols for extra information - (s) solid, (L) liquid, (g) gases, (aq) aqueous solutions - substance dissolved in water

  • In a balanced equation, there is the same amount of atoms on both sides

Crystallisation

  • Crystallisation - when crystals start to form

  1. Crush using pestle and mortar - increase surface area, speed up dissolving

  2. Add water to dissolve soluble substances

  3. Filter to remove insoluble substances

  4. Heat to remove water - stop at point of crystallisation

Alkali Metals

Alkali Metals

Other Metals

o Very soft - can be cut with knife

o Not very dense - float on water

o Reactive so must be stored in oil

o Conducts electricity and heat

o Shiny then dull

o Low melting and boiling points

o Used in building materials

o Conduct heat and electricity

o Shiny

o High melting and boiling points

Reactivity of Alkali metals

As you go down the group:

  • The number of shells increase

  • Weaker nuclear attraction

  • Easier to lose outer electron

Halogens

  • They are called Halogens when in atom form and Halide when in ion form

  • Displacement is the reaction where an element is replaced by a more reactive element

  • A halide has a full outer shell while a Halogen doesn’t

  • A Halogen will displace any halogen below it in the group

As you go down group 7:

  • There are more electrons

  • Stronger intermolecular forces

  • Requires more energy to break intermolecular forces

  • Higher melting / boiling points

Transition Metals

  • They have high melting points, are good conductors, strong, very dense

  • Transition metal are in the middle of the table

  • Transition metal have low reactivity

  • Transition metal can form different ions and each ion is a different colour

  • Transition metal can be used for catalysts for reactions in hydrogenation, or structural materials replace joint