C4 - Chemical Patterns

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Atoms & Line Spectrums

Atoms

Number protons = number electrons -> electrons added/removed -> changes charge

Neutrons -> neutral (0) -> relative mass: 1

Protons -> posotive (+1) -> relative mass: 1

Decides element

Same no. protons -> same element

Diff no. protons -> diff. element

Elements -> diff. properties -> diff. atomic structure

Electrons -> negative (-1) -> relative mass: 0.0005

No mass

Negative Charge

Tiny -> cover lots of space

Size of atom depends on volume of orbit

Move around nucleus

Arranged in shells (energy levels)

Nucleus

Whole mass concentrated

Contains protons & neutrons

Overall positive charge (protons)

Middle of atom

Line Spectrums

Lithium (Li) -> red flame

Sodium (NA) -> yellow/orange flame

Potassium -> lilac flame

What it is:

Electrons heated -> release energy as light

Wavelength emitted -> recorded as line spectrum

Diff elements -> diff wavelengths -> each element has diff electron arrangments

Used to identify elements -> spectroscopy

Examples:

Caesium & rubidium -> discovered by line spectrum

Helium -> line spectrum of Sun

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History of Periodic Table & Modern Periodic Table

History of Periodic Table

1800s:

Only thing measurable -> relative atomic mass

Known elements organised in order of atomic mass

1828 -> Dobereiner:

Made: list elements in groups based on chemical properties

Groups of 3 (triads)

Middle element of triad had relative atomic mass -> average of other 2

1865 -> Newlands' Law of Octaves:

Realised: when elements arranged in relative atomic mass -> every 8th -> similar properties

1865 -> presented theory to Chemical Society

Criticised because:

Mixed metals & non-metals

Groups contained elements with no similar properties

Didn't leave gaps for undiscovered elements

1869 -> Dimitri Mendeleev:

Arranged Table of elements w/ various big gaps

In order of atomic mass

Kept elements w/ similar properties in vertical groups

Predicted properties of undiscovered elements

When found -> fitted patterns (confirmation)

Modern Periodic Table

Proton number -> no. protons & electrons in nucleus

Relative atomic mass -> no. protons & neutrons

Neutrons = no. protons - relative atomic mass

Rows -> periods -> represents full shell

Metals -> left

Non-metals -> right

Similar properties -> columns -> groups

Group number -> no. electrons in shell (group 0 -> 8 electrons)

Group 1 -> react more vigorously going down

Group 7 -> reactivity decreases going down

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Electron Shells, Ionic Bonding & Ions and Formulas

Electron Shells

1) Lowest shells always filled 1st:

1st shell: 2

2nd shell: 8

3rd shell: 8

2) Atoms want outer shell to be full

Ionic Bonding

Group 1 lose electron -> posotive ion

Group 7 lose electron -> negative ion

How are Ionic Bonds made?

Atoms lose/gain electrons -> form charged particles -> ions

Can be made from single atom (Cl-) or group of atoms (NO3-)

Atoms lose/gain electrons -> trying to gain full outer shell

Transferring Electrons

Oppositely charged ions -> strongly attracted

Ionic Compounds

Solid ionic compounds -> giant lattice of ions

Each lattice -> single crystal

Become molten/dissolved -> conduct electricity -> because ions able to move

Ions and Formulas

Diff ions -> diff charges

No. in brackets -> size of positive charge on ion (e.g Iron(II) -> charge of 2+ -> Fe 2+)

In compounds -> total charge always add up to zero

If ions in compound have same size charge it's easy -> e.g Li+ & F- = LiF

If ions have diff size charges -> put in some no.s to balance -> e.g Ca2 & Cl- =CaCl2

If know formula & charge on one of the ions -> can work out charge of other ion -> e.g LiBr - Br1- = Li+1

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Group 1 - Alkali Metals & Group 7 - Halogens

Group 1 - Alkali Metals

Include: lithium, sodium, potassium

All have 1 outer shell -> very reactive & similar properties

Alkali metals react -> form similar compounds

Shiny when freshly cut -> quickly react with O2 in moist air

Go down group 1 -> more reactive

Outer electron is more easily lost -> further away from nucleus

Higher density -> atoms have more mass

Lower melting point

Lower boiling point

Reaction with cold water produces hydrogen gas

Lithium/Sodium/Potassium -> in water -> react very vigorously

Move around surface -> fizzing furiously

Produce hydrogen gas

Potassium -> hot enough to ignite -> lighted splint indicate hyrdrogen -> "squeaky pop"

Reaction makes alkali solution -> hydroxide of metal forms e.g sodium hyrdroxide (NaOH), potassium hyrdroxide (KOH) etc

More violent reaction -> more reactive alkali metal is

Reaction with chlorine produces salt

Alkali metals -> react vigorously w/ chlorine

Produces colourless crystalline salts e.g lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl)

Group 7 - Halogens

Include: chlorine, bromine, iodine

7 outer shells -> very reactive & similar properties -> form similar compounds

Form diatomic molecules -> pairs of atoms

Go down group 7 -> less reactive

Outer electrons -> further from nucleus -> additional electrons -> attracted less strongly

Higher melting point

Higher boiling point

Go from gases to solids down group -> shows trend in melting & boiling point

e.g chlorine more reactive than bromine which more reactive than iodine

Coloured vapours at room temp & pressure

Fluorine -> very reactive -> poisonous yellow gas

Chlorine -> fairly reactive -> poisonous dense green gas

Bromine -> dense -> poisonous -> orange volatile liquid -> orange gas

Iodine -> dark grey crystalline solid at room temp -> purple vapour

Reactions with alkali metals

Form salts -> metal halides

Reactions less vigorous as go down

Reactions with iron

Form coloured solids -> iron halides

Reactions less vigorous as go down

Displacement Reactions

More reactive element 'pushes out' (displaces) less reactive element from a compound

e.g chlorine more reactive than iodine -> chlorine reacts with potassium iodide solution -> form potassium chloride -> iodine left in solution

e.g chlorine displace bromine from solutions of bromide & bromine displace iodine -> because trend of reactivity

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Safety of Alkali Metals and Halogens

Alkali Metals

Really reactive -> combust spontaneously

Contact w/ water vapour in air -> violent reaction -> depending how much alkali metal present

Stored under oil to prevent violent reaction

Never touched with bare hands -> sweat on skin enough cause reaction -> produce lots of heat & corrosive hydroxide

Every piece of apparatus -> completely dry

Halogens

Chlorine & iodine -> very toxic

Fluorine -> most reactive halogen -> too dangerous use in lab

Liquid bromine -> corrosive -> avoid contact w/ skin

Poisonous vapours -> irritate respiratory system & eyes -> used in fume cupboard