5.1.1 - A Simple Model Of The Atom, Symbols, Relative Atomic Mass, Electronic Charge And Isotopes Flashcards
What are all substances made of
Atoms
What is an atom
The smallest part of an element that can exist
What are atoms of each element represented by
A chemical symbol (eg = Na or O)
How are compounds formed
From elements by chemical reactions
What do chemical reactions always involve
- The formation of one or more new substances
- a detectable energy change
What do compounds contain
Two or more elements chemically combined in fixed proportions
How are compounds represented
By formulae using the symbols of the atoms from which they were formed
What’s the only way compounds can be separated into elements
By chemical reactions
What does a micture consist of
Two or more elements/compounds not chemically combined together
What are the chemical proportions of each substance in a mixture like
Unchanged
How can mixtures be separated + examples
By physical processes
Eg = filtration, crystallisation, simple distillation, fractional distillation and chromotography
What do the physical processes for mixtures being separated not involve
Chemical reactions
No new substances are made
What does filtration separate
An insoluble solid from a liquid
What is filtration useful for separating
Separating sand from a mixture of sand and water OR an excess reactant from a reaction mixture
Why does filtration work
The filter paper has tiny holes/pores in it - they’re large enough to let small molecules + dissolved ions through but not larger particles of the un dissolved solid
Steps to filtration
1) one beaker has a micture of solid and liquid, the other has a funnel with filter paper in it
2) the solid and liquid mixtures poured into the filter funnel
3) the liquid drips through the filter paper but the solid particles are caught in the filter paper
What is crystallisation used for
To produce solid crystals from a solution
How does crystallisation work
When the solutions warmed, so,e of the solvent evaporates leaving crystals behind
Example of when crystallisation is used
To obtain copper Sulfate crystals from copper Sulfate solution
Steps to crystallisation
1) a solutions placed in an evaporating basin and heated with a Bunsen burner
2) the volume of the solution has decarsed because some waters evaporated - solid particles begin to form in the basin
3) all the water evaporates and leaves solid crystals behind
What’s simple distillation used for
To separate a solvent from a solution
What’s simple distillation useful for
For producing pure water from seawater
How does simple distillation work
- The dissolved solute has a much higher boiling point than the solvent
- when the solutions heated, solvent vapour leaves the solution
- it moves away and is cooled/condensed
- the remaining solution becomes more concentrated as the amount of solvent in it decreases
Steps to simple distillation
1) salty waters heated
2) the water vapour cools in the condenser and drips into a beaker
3)the waters condensed and is now in the beaker, the salt stays behind
What’s fractional distillation used to separate
To separate different liquids from a mixture of liquids
What’s fractional distillation useful for separating
Ethanol from a mixture of ethanol and water AND separating different fractions from crude oil
Why does fractional distillation work
Because the different liquids have different boiling points
How does fractional distillation work
When the mixtures heated -
1) vapour rises through a column which is hot at the bottom and cooler at the top
2) vapours condense when they reach the part of the column that’s below the temperature of their boiling point
3) each liquids led away from the column
What are the two ways to obtaining different liquids from the column
1) by collected different liquids from different parts of the column - the substance with the lowest boiling points collected at the top of the column
2) by continuing to heat the mixture to increase the temperatures in the column - the substance with the lowest boiling points collected first
Steps to fractional distillation
1) water and ethanol solution is heated
2) the ethanols evaporates first, cools and then condenses
3) the water left evaporates cools and then condenses
What does Papier chromatography separate
Mixtures of soluble substances - often coloured substances (eg = food colourings, inks, dyes or plant pigments)
What are the two phases in chromatography
- stationary phase = paper
- mobile phase = the solvent
What does a pure substance produce in chromatography
One spot
What does an impure substance produce in chromatography
Two or more spots
How do you know if two substances are likely the same in chromatography
- if they produce the same number of spots and they’re the same colour
- if the spots travel the same distance up the paper
What may lead to a scientific model being changed/replaced
New experimental evidence
What were atoms thought to be before the discovery of the electron + by who
Tiny spheres that couldn’t be divided
- by john dalton at the start of the 19th century
What discovery led to the plum pudding model
Discovery of the electron
Who + what year was the plum pudding model
1897 - J.J Thompson
What did the plum pudding model suggest
That the atoms a ball of positive charge with negative electrons embedded into it
Who + when was the alpha particle experiment
1909 - Ernest Rutherford
What conclusion did the alpha particle scattering experiment lead to
- The mass of an atom was concentrated/positively charged at the centre (nucleus)
- a ‘cloud’ of negative electrons surround the nucleus (most of the atoms empty space)
What model replaced the plum pudding
Alpha particle scattering experiment
What did the particles do in the alpha particle experiment
- most when straight through the gold sheet
- some were deflected at large angles
- a small number were deflected backwards
What did Niels bohr suggest about the atom
That the electrons orbit the nucleus at specific distances
What did later experiments lead to
The positive charge of any nucleus could be divided into smaller particles that have the same positive charge - the proton
What did James Chadwick show the existence of + when
The neutrons within the nucleus about 20 years after the nucleus became an accepted scientific idea
The relative charges of
1) proton
2) electron
3) neutron
1) +1
2) -1
3) 0
What’s the number of electrons equal to
The number of protons
Do atoms have an overall electrical charge
No
What is the atomic number
The number of protons in an atom
What do all atoms of a particular element have
The same number of protons
What is an atoms radius
0.1 nm (1x10^-10 nm)
What is the nucleus radius
1 x 10^-14 m)
Where’s almost all the mass in an atom
The nucleus
Relative masses of
1) proton
2) neutron
3) electron
1) 1
2) 1
3) very small (1/2000)
What is the sum of protons and neutrons in an atom
The mass number
What’s an isotope
The same elements each with a different number of neutrons
What is the top number
The mass number
What’s the bottom number
The atomic number
How to find out how many neutrons are in an element
Atomic number - mass number
What’s the relative atomic mass
An average mass that takes into account the different masses/abundances of all the isotopes of the element
How to find the relative atomic mass
Sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes
What do electrons move around the nucleus in
In electron shells
How were elements originally arranged
By their atomic weight
What was bad about elements being in order of atomic weight
Periodic tables weren’t complete and many elements were placed in the wrong group
What did Mendeleev do with the periodic table in 1869
- he left gaps for elements that hadn’t been discovered yet
- put the elements in order of atomic weht but moved them round if their properties meant it should be changed
What happened with the gaps he left in the table
Elements with properties predicted by him were discovered and they filled i the gaps
What did the knowledge of isotopes explain
Why the the order based on atomic weight wasnt always correct
What are metals
Elements that react to form positive ions
What are non-metals
Elements that dont form positive ions
Physical properties of a metal
- strong but malleable
- good at conducting heat/electricity
- high boiling/melting points
Physical properties of non-metals
- dull
- brittle
- aren’t always solids at room temperature
- don’t conduct electricity
- lower density
Why do non-metals have different properties to metals
They don’t have metallic bonding
How do atoms react to form a full outer shell
By losing, gaining or sharing electrons
Why do some metals feel a weaker attraction to their nucleus
They don’t have many electrons to remove OR they’re far away from the nucleus
What does a weaker attraction to the nucleus mean (to do with energy)
Not much energys needed to remove the electrons
Why is forming positive ions for non-metals difficult
They have lots of electrons to remove to get a full outer shell OR they’re outer electrons are close to their nucleus so they feel a strong attraction to it
What is the name for group 0
Noble gases
Why are group 0 unreactive + don’t form molecules easily
They have full outer shells
What happens to the boiling point as you go down the noble gases
Increases
Why do the noble gases increase in boiling point
An increase in the number of electrons leads to greater intermolecular forces
Order if noble gases from smallest boiling point to highest
Helium
Neon
Argon
Krypton
Xenon
Radon
What are group 1 elements called
The alkali metals
What happens as you go down the alkali metals
Increases reactivity
Lower melting/boiling points
Higher relative atomic mass
Why are the alkali metals very reactive
They have one outer electrons to remove in their outer shell
Why does tye reactivity increase in the alkali metals
The outer electrons more easily lost because the attraction between the nucleus and electron gets weaker - electrons further away from nucleus as you go down group
Properties of alkali metals
Soft
Low density
What happens when group 1 metals react with water
- react vigoursly to produce hydrogen gas and metal hydroxides
- as you go down the group the reactions get more vigorous
- as yiu go down the group the amount of energy given out increases
What happens when group 1 reacts with chlorine
- they react vigorously when heated in chlorine gas to form white metal chloride salts
- as you go down the group the reactions get more gets more vigorous
What happens when group 1 reacts with oxygen
- they form a metal oxide
What are group 7 known as
Halogens
Why do the halogens have similar reactions
They all have seven electrons on their outer shell
What happens as you go down the halogens
- less reactive
- higher melting/boiling points
- higher relative atomic mass
Why do the halogens become less reactive
It’s harder to gain a full outer shell because the outer shells become further away from the nucleus
How can halogens get a full outer shell
By sharing electrons by covalent bonding with other non-metals
What do the compounds that are formed when halogens react with the non-metals have
Simple molecular structures
In ionic bonding with halogens and metals what do the compounds formed have
Ionic structures
What can a displacement reaction occur between
A more reactive halogen and the salt of a less reactive one
