C1 - Atomic Structure and the Periodic Table

Element

substance with only one type of atom

Compound

2 or more different elements combined in fixed proportions

Molecule

2 or more atoms bound together

Mixtures

2 or more elements not chemically combined together

e.g., oil and water

Methods to separate mixtures

filtration

crystallisation

simple distillation

fractional distillation

chromatography

Simple Distillation

separates liquid from a solution

liquid boiled to gas

vapour rises from flask into condenser

cooled by cold water back into liquid

collected into second flask

dissolved solids left in first flask

Fractional Distillation

separates liquids with different boiling points and are miscible

mixture heated and boiled

vapour enters fractioning columns

rise, condense, drip back into flask, re-evaporate

lower boiling point liquid rises first to condenser and into flask

Fractional distillation:

Why are glass beads used?

increase separation efficiency by increasing surface area for evaporation and condensation 

Filtration

separates insoluble solid from liquid

e.g., sand and water

solid gets stuck on filter paper

Crystallisation

separates soluble solid in liquid

e.g., seawater 

bunsen burner lit

liquid evaporates 

solid crystals left behind 

Chromatography

separates mixtures of soluble substances

stationary phase - absorbent paper

mobile phase - solvent, moves through paper and carries substances

different substances within mixture attracted to each phase in different proportions - so will move to different extents up the paper

Ideas of modelling the atom - Past to Present

Plum-pudding

Nuclear 

Bohr 

Chadwick 

Plum-Pudding Model of an Atom

ball of + charge

electrons embedded within

Nuclear model of an atom

alpha particles directed at gold foil

under vacuum conditions 

most went straight through - most of an atom is empty space

small number delfected at large angles - concentration of + charge

Bohr model of the atom

electrons orbit nucleus at specific distances away (shells)

explains patterns of different elements burning differently

What is in an atom?

electrons

protons

neutrons

What is in the nucleus of an atom?

protons

neutrons

How are electrons arranged in?

shells/energy levels

Atomic number

number of electrons which = number of protons

Why does the number of electrons = number of protons in an atom?

atoms have neutral charge

Mass number =

number of protons + protons

Number of Neutrons in an atom =

mass number - atomic number

Isotopes 

atoms of the same element

same number of protons and electrons

different number of neutrons 

What is the Relative Atomic Mass of an atom?

average mass number of an atom of an element

Formula for Relative Atomic Mass =

sum of (isotope mass x abundance) / 100

Maximum number of electrons in 1st shell

2

Maximum number of electrons in 2nd shell

8

Maximum number of electrons in 3rd shell

8

Elements in the same group (column) in the periodic table have the same number of….

outer shell electrons

Elements in the same period (row) of the periodic table have the same number of….

shells

Why are noble gases (group 8/0) unreactive?

full outer shells of electrons 

energetically stable

Early Ideas of the period table: How did scientists classify elements? (Before the discovery of sub-atomic particles)

In order of atomic weight (relative atomic mass)

incomplete - many elements unknown

How did Dmitri Mendeleev change the periodic table?

Accounted for properties of elements

gaps in the table for unknown elements - predicted properties of these!

How are metals different from non-metals?

metals loose electrons = positive ions

How do non-metals differ from metals?

gain electrons = negative ions

Group 1 metals

form +1 ions

low density

stored under oil - prevents reacting with O and water

reactivity increases down group

Why does the reactivity in group 1 metals increase down the group?

atoms get larger

outer electron further away from the nucleus 

less attraction between the 2 

more easily lost

Group 1 reactions with non metals form…

ionic compounds

Group 1 reactions with water

metal hydroxides

fizzing 

reactivity increases down group

Group 7 non-metals (Halogens)

7 outer electrons

coloured vapours

diatomic molecules

less reactive down group

Why does reactivity of group 7 non-metals decrease down the group?

higher molecular mass

stronger intermolecular forces

higher boiling/melting points

Group 7 Displacement Reactions

more reactive halogens displace less reactive halogens in reactions

Transition Metals

ions with different charges

form coloured compounds

useful catalysts

hard

strong

high densities and melting points