Topic 1: Atomic Structure and the Periodic Table Flashcards
What is an atom?
The smallest part of an element that can exist
Proton:
i) mass
ii) charge
i) 1
ii) +1
Neutron:
i) mass
ii) charge
i) 1
ii) 0
Electron:
i) mass
ii) charge
i) very small
ii) -1
What is the number of protons equal to?
The number of electrons
What does atomic number show?
Number of protons
What does the mass number show?
Number of protons + neutrons
What is an ion?
An atom without charge
What is an isotope?
Different forms of the same element with the same number of protons but a different number of neutrons
How do you calculate relative atomic mass?
(isotope abundance x isotope mass number) / sum of abundance of all isotopes
What is a molecule?
Two or more atoms, held together by a chemical bond
What is a compound?
Two or more different elements, held together by chemical bonds
What is a mixture?
Two or more substances, not chemically bonded
In chromatography, why should the line be drawn with pencil?
Pencil marks are insoluble so won’t dissolve in the solvent
In chromatography, why should you make sure the ink isn’t touching the solvent?
To stop the ink dissolving into it
What is chromatography used to do?
Separate substances in a mixture
What is filtration used to do?
Separate insoluble solids from liquids
What is evaporation used to do?
Separate soluble solids from solutions
What is crystallisation used to do?
Separate soluble solids from solutions
When does crystallisation have to be used instead of evaporation?
If the salt decomposes when it’s heated
Explain how you would separate rock salt using filtration and crystallisation [4]
- Grind the rock salt to make sure the salt crystals are small, so will dissolve easily
- Put the mixture in water and stir - salt will dissolve, but the sand won’t
- Filter the mixture - the sand will collect on the paper but the salt will pass through in the solution
- Evaporate the water from the salt so that it forms dry crystals
What is rock salt a mixture of?
Sand and salt
What is simple distillation used to do?
Separate out solutions
What is the problem with simple distillation?
It can only be used to separate liquids with very different boiling points
What is fractional distillation used to do?
Separate a mixture of liquids
What did the atomic theory (Democtritus) state? [2]
- Everything is made from tiny particles, which can’t be broken down any further
- They are separated by empty space
What did John Dalton conclude? [2]
- Atoms were solid spheres
- Different types of spheres make up the different elements
What did the plum pudding model (J.J. Thomson) state?
The atom is a ball of positive charge with electrons stuck in it
Desscribe Rutherford’s gold foil experiment and the results [3]
- Fired alpha particles at thin gold foil
- Expected particles to pass straight through or only be slightly deflected
- Although most particles passed straight through, some were deflected more than expected and some were deflcted back the way they had come
What was concluded as a result of the gold foil experiment and why? [2]
- Atoms contain a compact, positive nucleus in the centre - because some of the particles were deflected back
- Rest of the atom is empty space - nearly all of the particles passed straight through
What was the model of the atom known as after the gold foil experiment?
Nuclear model
What did Bohr add to the nuclear model?
Electrons orbit the nucleus at specific distances
What did Chadwick discover?
The presence of neutrons in the nucleus
How many electrons maximum in the 1st shell?
2
How many electrons maximum in the 2nd shell?
8
Elements in the same group in the periodic table have what in common?
Same number of electrons in their outer shell (similar chemical properties)
How were elements classified in the early 1800s?
By atomic wight
What 2 changes did Mendeleev make to the early periodic table?
- He left gaps in order to keep elements with similar properties in the same group
- He switched the order of elements based on their properties, even if their atomic weights were no longer in order
What made it possible to explain why the order based on atomic weights is not always right on the periodic table?
The discovery of isotopes in the early 20th century
What kind of ions do metals form?
Positive ions
What kind of ions do non-metals form?
Not positive ions
Physical properties of metals [3]
- Malleable
- Great conductors of heat and electricity
- High boiling and melting points
Physical properties of non-metals [4]
- Dull in colour
- Brittle
- Poor conductor of electricity
- Low boiling and melting points
What special properties do transition metals have? [3]
- Elements can form more than one ion
- Ions are often coloured
- They make great catalysts
What is another name for group 1 metals?
Alkali metals
Alkali metal properties [3]
- Soft
- Low density
- Low melting point
Alkali metal trends [2]
- Increasing reactivity
- Decreasing melting and boiling points
What do the alkali metals form with non-metals?
Ionic compounds
Ionic compounds:
i) colour and state
i) colour in water
i) white solids
i) form colourless solutions
What does alkali metal + water produce?
Metal hydroxide + hydrogen gas
What does alkali metal + chlorine produce?
Metal chloride salts
What does alkali metal + oxygen produce?
Metal oxides
Lithium + oxygen forms?
Lithium oxide
What is the formula for lithium oxide?
Li₂O
Sodium + oxygen forms? [2]
- Sodium oxide
- Sodium peroxide
What is the formula for sodium oxide?
Na₂O
What is the formula for sodium peroxide?
Na₂O₂
Potassium + oxygen forms? [2]
- Potassium peroxide
- Potassium superoxide
What is the formula for potassium peroxide?
K₂O₂
What is the formula for potassium superoxide?
KO₂
What is another name for group 7?
Halogens
Halogen trends [2]
- Decreasing reactivity
- Increasing melting and boiling points
What will a more reactive halogen do?
Displace a less reactive one
What is fluorine?
Yellow gas
What is chlorine?
Green gas
What is bromine?
Red-brown liquid
What is iodine? [2]
- Grey solid
- Purple vapour
What is another name for group 0?
Noble gases
Noble gas properties [3]
- Colourless gases
- Unreactive
- Non - flammable
Noble gas trend
Increasing melting and boiling points
How do group 1 metals differ to transition metals? [3]
- More reactive
- Less dense, strong, hard
- Lower melting points