Chemistry Topic 2 - Atomic structure, periodic table, Groups 1,7,8 (Year 9 Autumn 2)

Describe how Dalton's ideas about atoms have changed

Dalton's ideas helped explain some properties of matter but research shows atoms contain subatomic particles (electrons)

Describe how the subatomic particles are arranged in an atom.

Atoms in an element always have and equal number of protons and electrons - no overall charge

proton: relative charge and mass

Relative Charge: +1

Relative mass: 1

neutron: relative charge and mass

Relative charge: 0

Relative mass: 1

electron: relative charge and mass

Relative charge= -1

Relative mass: 1

Describe how the size of an atom compares to the size of its nucleus

the diameter of an atom can be 100,000 times bigger than the diameter of the nucleus

State where most of the mass of an atom is found

the nucleus of an atom because the mass of an electron is described as negligible

Atomic number

the number of protons in an atom

Mass number

number of protons + neutrons

isotope

atoms of the same element with the same number of protons (atomic number) but a different number number of neutrons (mass number)

Relative Atomic mass

average mass of all isotopes in an element on a scale compared with carbon 12

Relative atomic mass equation

Ar = (isotope abundance x mass number) …. / 100

How did Mendeleev arrange elements in his periodic table

by increasing relative atomic mass

Describe how Mendeleev predicted the existence and properties of some elements yet to be discovered.

by leaving gaps in his table to make prediction about the properties of undiscovered elements.

Explain how Mendeleev's early ideas were supported by later evidence.

Many of his prediction were correct after discovered.

He successfully predicted the properties of: eka-aluminium, gallium, scandium …..

What problems did Mendeleev face

since ordering elements with atomic mass it lead to inconsistencies forcing him to swap elements.

how are elements arranged in the modern periodic table

increasing atomic number

Elements in a group

elements in a groups have similar properties

where are non-metals and metals located on the periodic table

non-metals are on the right side of the table

electronic configuration

the arrangement of electrons in shells of an atom

electronic configuration rule

1st Shell - up to 2

2nd Shell - up to 8

3rd Shell - up to 8

link between element's position in the periodic table and electronic configuration

number of occupied shells = period number

number of valence electrons = group number

Alkali metals - physical properties

-shiny, soft

-easy to cut

-highly reactive

-easily oxidised, burn brightly in air

how to alkali metals react with oxygen

example: potassium + oxygen > potassium oxide

how to alkali metals react with water

react with water to form metal hydroxide and hydrogen

E.g. alkali metal + water > metal hydroxide + hydrogen

reactivity of alkali metals

increases as you go down the group beacause the valence electron (1) gets further from the nucleus and easier to remove

appearance of halogens at room temperature

GAS- fluorine and chlorine

LIQUID - bromine

SOLID - iodine and astatine

halogen - trend in colour

colours become darker and deeper as you go down the group

halogen - melting and boiling point trend

melting and boiling point increases as you go down the group

what kind of molecule are halogens

halogens exist as diatomic molecules, with 2 atoms held together by a single covalent bond

Test for Chlorine

depends on the bleaching action:

When damp blue litmus paper is places in chlorine gas it first turns red then bleaches white

how do halogens react with metals

by forming salts which contain halide ions

chlorine + magnesium > magnesium chloride (halide salt)

how do halogens react with hydrogen

to form HYDROGEN HALIDES which dissolve in water to form acidic solutions

-hydrogen + chlorine > hydrogen chloride (dissolves in water to make hydrochloric acid)

halogen reactivity trend

decreases down the group

-atoms of each element get larger going down making the outer shell further away from the nucleus and shielded by more electron shells

-the further the outer shell the harder to attract another electron

Displacement Reactions

When a more reactive element takes place of a less reactive element

-chlorine + sodium bromide > bromine + sodium chloride (chlorine displaces bromine)

oxidation

loss of electrons

reduction

gain of electrons

Redox

when oxidation and reduction occur at the same time in displacement reactions

ion

an atom or molecule that has lost or gained an electron giving it a positive or negative electrical charge

why do noble gases not react easily

they are inert because they have a full outer shell which gives them a stable electronic configuration

noble gases trends (physical properties)

-colourless

-low melting/boiling points

-poor conductors of heat/electricity

-exist as single atoms because they don't form bonds easily

-only small amounts of each gas in the atmosphere

examples of the uses of noble gases

-HELIUM is used for weather balloons +airships because it has low density and non-flammable

-NEON is used in long lasting illuminated signs because it gives off a red/orange light when energy passes through