Paper 1 Flashcards
Why do isotopes have the same chemical properties?
This is because they contain the same number of electrons. Electrons determine chemical properties of atoms.
John Dalton
John Dalton described atoms as tiny spheres that could not be divided
JJ Thomspson
- J.J. Thomson discovered the plum pudding model
- It is a ball of positive charge with electrons embedded in the ball of positive charge.
- No empty space in the atom
- Mass spread throughout
Ernest Rutherford:
- Ernest Rutherford’s alpha scattering experiment led to the plum pudding model being replaced by nuclear model.
- Positive charge concentrated at the centre
- Most of the atom is empty space
- Mass is concentrated at the centre
Niels Bohr
- Niels Bohr adapted the nuclear model by suggesting that the electrons orbit the nucleus at specific distances.
- The electrons are on electron shells/energy level.
Later experiments:
- Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge.
- The name proton was given to these particles.
- James Chadwick provided the evidence for the existence of neutrons in the nucleus.
- This was about 20 years after the nucleus became an accepted scientific idea.
- This could help explain the existence of isotopes.
Modern periodic table
- Arranged in order of atomic number, elements with similar properties are in columns, known as groups.
- Periodic table- siimilar properties occur at regular intervals.
- Elements in same group - same number of electrons in their outer shell- gives them similar chemical properties.
- Elements in the same period have the same number of electron shells
- As you go down the group, the number of shells increases.
- Metals are found on the left-hand side of the periodic table whilst non-metals on the right-hand side
- Most of the elements found on the period table are metals
Properties of metals:
- High density
- High melting point
- Shiny
- Malleable
- Conducts electricity and heat
Properties of non-metals:
- Low density
- Low melting point
- Dull
- Brittle
- Does not conduct electricity nor heat
What were early periodic tables arranged in order of?
In order of atomic weight.
Newland’s periodic table:
- Have more than one element in a box
- Missing Noble gases
- Arranged elements in order of atomic weight
DISADVANTAGES:
* He did not leave gaps for undiscovered elements
* He had many dissimilar elements in a column
Mendeleev’s periodic table:
- Have more than one element in a box
- Missing Noble gases
- Arranged elements in order of atomic weight
Advantages of Mendeleev
* He left gaps for undiscovered elements
* He changed the order of some elements
Why was Mendeleev’s periodic table accepted?
- He predicted properties of missing elements
- Elements with properties predicted by Mendeleev were discovered
- Elements were discovered which fitted the gaps
Group 0 (Nole gases)
- Noble gases exist as single atoms (monoatomic) as they have a full outer shell, which means they do not lose or gain electrons.
- They are unreactive because they have a full outer shell and they do not need to lose
or gain electrons. - The boiling points of the noble gases increase with increasing relative atomic mass (going down the group).
Group 1 metals:
- They react with non-metals to form ionic compounds
- The compounds are white solids which dissolve in water to form colourless solutions.
- The alkali metals all have low densities.
- The first three alkali metals (Li, Na & K) are all less dense than water – this is why they float on the surface.
Observation of the first three alkali metals with water
- The alkali metals react with water to form a metal hydroxide and hydrogen gas.
- When universal indicator is added to the metal hydroxide solution, it turns purple as it contains OH-(hydroxide) ions.
Lithium reaction with water:
- Fizzing/ bubbles
- Moves on the surface of the water
- Gets smaller in size
Sodium reaction with water:
- Fizzing/ bubbles
- Moves quickly on the surface of water
- Gets smaller in size
Potassium reaction with water:
- Fizzing/ bubbles
- Moves very quickly on the surface of water
- Gets smaller in size
- Lilac flame
Why does the reactivity of group 1 metals increases down the group?
- More electron shells down the group
- Weaker attraction between the nucleus and the outer shell electron
- Easy to lose the outer electron
Halogens:
- All have 7 electrons on their outer shell
- They have coloured vapours
- Consist of molecules which are made up of pairs of atoms (diatomic) For example, Cl2, F2, Br2
Why does the melting point and boiling point increase down group 7?
- The melting and boiling point increases as you go down group 7 because the relative molecular mass increases.
Why does reactivity decrease down group 7?
- More electron shells
- Weaker attraction between the nucleus and the outer shell electron
- Harder to gain an electron
Halogen- displacement reaction:
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
Compared with group 1 elements, the transition metals:
- Have higher melting points
- Have higher densities
- Are stronger
- Are harder
- Are muss less reactive- so do not react as vigorously with water and oxygen
Properties of transition metals:
- Have ions with different charges
- Form coloured compounds
- Are useful as catalysts
Atoms:
- All substances are made of atoms.
- An atom is the smallest part of an element that can exist.
Element:
A substance made form one type of atom
Compounds:
- Contains atoms of two or more different elements chemically bonded together.
- Is difficult to separate.
Mixture:
- A mixture is when two or more different elements or compounds that are not chemically bonded together.
Key definitions- seperation techniques:
- Soluble – it dissolves.
- Insoluble – it will not dissolve. Examples of insoluble substances include mud and sand.
- Solute – a solid being dissolved. Example include salt and sugar.
- Solvent – a liquid a solute can be dissolved into.
- Solution – a mixture of a solute and solvent that does not separate.
Filtration:
Used to seperate an insoluble solid from a liquid
Simple distillation:
- Used to seperate liquids with very diffferent boiling points
- Used to seperate a liquid from a soluble solid
Fractional distillation:
Used to seperate solutions with similar boiling points