Atomic Structure and the Periodic Table Flashcards
What are compounds?
Compounds contain two or more elements CHEMICALLY COMBINED
Half equations and Ionic Equations
!!!
How can mixtures be separated?
Because they are not chemically bonded, they can be separated through physical processes, such as filtration, crystallisation, simple distillation, fractional distillation and chromatography
What are key factors when separating mixtures of solids?
Differences in density, magnetic properties, sublimation and solubility
For a difference in solubility, a suitable SOLVENT must be chosen to ensure that only the desired substance dissolves in the solvent and not the other substances or impurities
What are key factors when separating mixtures of liquids?
Immiscible liquids can be separated using a SEPARATING Funnel or by DECANTING (pouring carefully)
Eg. Oil and water or when an organic product is formed in aqueous conditions
However miscible liquids need to be separated by fractional distillation
What is filtration?
Used to separate UNDISSOLVED SOLID from a mixture of the solid and a liquid / solution (such as sand in a mixture of sand and water)
- It involves placing filter paper in a filter funnel above a beaker
- Then the mixture of insoluble solid (sand) and liquid (water) is poured into the filter funnel
- Filter paper will only allow small liquid particles to pass through as a filtrate
- So the solid particles too large to pass through will stay behind as a RESIDUE
- The insoluble solid (sand) and liquid (water) are separated
What is crystallisation?
Used to separate a DISSOLVED SOLID from a solution, when the solid is much more soluble in a HOT SOLVENT than in a COLD SOLVENT. (eg copper sulphate from a solution of copper (II) sulphate in water)
- The solution is heated, allowing the solvent to evaporate leaving a saturated solution behind
- One tests if the solution is saturated by dipping a clean dry, cold glass rod into the solution. If the solution is saturated, crystals will form on the glass rod
- The saturated solution is allowed to cool slowly
- Crystals begin to grow as solids will come out of a solution due to decreasing solubility
- The crystals are collected by filtering the solution, and then they are washed with cold distilled water to remove impurities then allowed to dry
What is simple distillation?
Used to separate a liquid and a soluble solid (eg. Water from as solution of salt and water
- The solution is heated and pure water evaporates producing a vapour which rises through the next and the round bottomed flask
- The vapour passes through the CONDENSER where it cools and condenses, turning into the PURE LIQUID that is collected in a beaker
- After all the water is evaporated from the solution, only the solid solute will be left behind
What is fractional Distillation?
Used to separate two or more liquids that are miscible with one another (eg. Ethanol and water from a mixture of the two)
- The solution is heated to the temperature of the substance with the LOWEST BOILING POINT
- This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
- All of the substance is evaporated and collected, leaving behind the other components of the mixture
- For water and ethanol, ethanol has a boiling point of 78 degrees C and Water of 100 degrees C
- So the mixture is heated til it is 78 degrees C at which point the ethanol boils and DISTILS out of the mixture and condenses into the beaker
- When the temperature starts to increase to 100 degrees C, the heating should be STOPPED, because water and ethanol are now separated
What is Paper Chromatography?
Used to separate substances that have DIFFERENT SOLUBILITIES in a given solvent (eg. Different coloured inks that have been mixed to make black ink)
- A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this because ink would run into the chromatogram along with the samples
- The paper is then lowered into the solvent container, making sure that the pencil line sits ABOVE the level of the solvent container so the samples dont wash into the solvent container
- The solvent travels up the paper by CAPILLARY ACTION, taking some pf the coloured substances with it
- Different substances have different solubilities so will travel at different rates causing the substances to spread apart, and these substances with HIGHER SOLUBILITY with travel FURTHER than others
- This will show the different components of the ink / dye
- If two or more substances are the same, they will produce identical chromatograms
- If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
- An impure substance will show up with more than one spot, and a pure substance would ONLY show up with ONE spot
What are the subatomic particles of an atom?
Protons, Neutrons and Electrons
How do electrons move around the nucleus?
Through orbital paths called SHELLS
What did John Dalton develop?
In 1803, John Dalton presented the BILLIARD BALL, where -
- Matter is made of atoms which are tiny particles that cannot be created, destroyed or divided
- Atoms of the same element are identical and atoms of different elements are different
- Different atoms combine together to form new substances
What happens when there is new evidence for a new scientific theory?
May lead to other scientific models being changed or replaced
What did J.J. Thompson develop?
1897 - The Plum Pudding Model.
He used a cathode ray-tube to identify electrons and prove that atoms are divisible
The plum pudding model stated that there were electrons embedded inside of the atom
What did Ernest Rutherford develop?
1909 - Nuclear Model of the Atom
Rutherford’s model consists mainly of empty space with the nucleus at the centre and the electrons orbiting the paths around the nucleus
He fired a beam of alpha particles at thin gold foil.
The fact most atoms passed through proves the atom is mostly empty space
Some atoms deflecting at an obtuse angle suggests atoms repelling at the centre of two positive nuclei
The fact the atoms bouncing back was rare, it suggests the nucleus was very small and so the chances of them colliding was low.
What did Niels Bohr develop?
1913 - The Bohr Model
He proposed that the electrons orbited the nucleus in fixed shells at set distances
Each orbital has a different energy associated with it, and the higher energy orbitals are located further away from the nucleus
Bohr’s work led to the discovery of the proton when he found that the nucleus could be divided into smaller parts
What did James Chadwick propose?
That there were neutral particles in the nucleus called neutrons
What happens to the energy when the shell is further away from the nucleus?
The further away the shell is, the more energy is has
What is the outermost electron called?
The valence shell
How does an atom become stable?
By gaining a full outer shell of electrons
Why are atoms neutral?
Because there are the same numbers of electrons and protons which cancel out to make a charge of 0
What are the masses of subatomic particles?
Neutron - 1
Proton - 1
Electron - Negligible
What is the atomic number?
The number of protons in the nucleus of the atom.
It is also the position of the element in the periodic table
What is the mass number?
The total number of protons and neutrons in the nucleus of an atom
What are Isotopes?
Atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
What is different about the chemical characteristics of isotopes?
Nothing, they display the same chemical characteristics
What are the vertical columns in the periodic table called?
Groups
What are the horizontal rows in the periodic table called?
Periods
What happens to the reactivity of group 1 metals as you move down the group?
Reactivity increases
What happens to the reactivity of group 7 non-metals as you move down the group?
Reactivity decreases
What are covalent compounds?
Compounds with only non metals in it
What are ionic compounds?
Compounds with metal and non-metal elements joined
In earlier models of the periodic table, how did scientists arrange the elements?
In order of their atomic masses and NOT THEIR ATOMIC NUMBER, which were incomplete because not all elements were discovered, causing elements to be placed in the wrong group
What did Dmitri Mendeleev do?
1869 - Created his first draft of the periodic table
- Organised them into vertical columns based on PROPERTIES
- Then arranged them HORIZONTALLY in order of INCREASING ATOMIC MASS
- He saw a pattern begin to appear in which chemically similar elements fell naturally into the same columns
- There were some exceptions due to lack of discovery of the whole periodic table
- Mendeleev worked to include all the elements, but he didn’t force an element to fit the pattern but he left GAPS in the table that would be fit by elements that WOULD BE DISCOVERED IN THE FUTURE
Mendeleev realised that elements should be placed in the same column, and he then realised the gaps must correspond to elements that had not been discovered.
So he used PROPERTIES of other elements in similar groups to PREDICT properties of undiscovered elements
One fall-back with Mendeleev’s periodic table was that there were still exceptions due to humans not knowing that ISOTOPES were, so there was some level of inaccuracy in his table
What types of elements form positive ions when they lose electrons?
METALSSSSSS
What types of elements form negative ions when they gain electrons
NON - METALLSSSSSS
What is an ion?
An atom or molecule which has become charged through the loss or gain of one or more electrons
What are positive ions called?
Cations
What are negative ions called?
Anions
What happens as you descend the groups?
The outer electrons become further away from the nucleus as the number of shells increase, which weakens their attraction to the nucleus
Properties of Non-Metals and Metals
Metals -
- High melting and boiling points
- Good conductors of heat and electricity
- Malleable
- Strong, hard
- Shiny, lustrous
Non-Metals -
- Low melting and boiling points
- Poor conductors of electricity and heat
- Different states at RT
- Brittle, flaky
What are the elements in group 0 known as?
Noble Gases
What is special about group 0?
All the elements have FULL OUTER SHELLS OF ELECTRONS so are INERT and UNREACTIVE
They are all non-metal, MONATOMIC, colourless, non-flammable gases at room temperature
What can Noble gases be used for?
Helium - filling balloons because it is less dense than air and is not flammable
Neon, argon and xenon - advertising signs
Argon - providing an inert atmosphere for WELDING, and also to fill light bulbs (because it glows brightly)
Properties of Noble gases?
- Very low melting and boiling points
- Show an INCREASE in boiling point as we move DOWN the group due to an increase in the AR
- They have very low densities because they are al gases so their atoms are widely spread apart. However their densities increase as you go down the group, as usual
Why do boiling points increase down the group for some groups, eg. Noble gases?
Increased intermolecular forces between atoms, which increases the amount of energy needed to overcome these forces to change state
What are group one metals called?
Alkali Metals (known as this because they form alkaline solutions when they react with water
What are the properties of the Alkali metals?
- All soft metals (get softer as you go down the group EXCEPT FOR POTASSIUM)
- Relatively low densities and boiling points- due to decreasing attractive forces between outer electrons and positive ions
- VERY Reactive
- Reactivity INCREASES as you go down the group (electron is further away so weaker forces of attraction so electron is easily lost)
Why do we store alkali metals in oil?
Because they react with the air (water vapour in the air)
How does lithium react with water? R
Relatively slow reaction, Lithium doesn’t melt, fizzing can be seen and heard as the lithium reacts
How does sodium react with water? R
Large amounts of heat released cause sodium to melt, hydrogen released catches fire and causes the ball of sodium to dash across the surface of the water
How does potassium react with water?
Reacts more violently than sodium, enough heat released so hydrogen burns with a lilac coloured flame, melts into a shiny ball that dashes around the surface
What is the equation when alkali metals react with oxygen? What happens visually?
(metal) oxide
eg. Sodium Oxide
A metal oxide coats the surface of the metal
What is the equation when alkali metals react with chlorine? What happens visually?
(metal) chloride
eg. Potassium Chloride
React vigorously when HEATED WITH CHLORINE GAS
What are the group 7 elements called?
The Halogens
What are properties of the Halogens?
- All poisonous non-metals
- All have similar reactions
- All are DIATOMIC, meaning they form molecules made of pairs of atoms sharing electrons
- Form halide ions with a -1 charge
- Melting and boiling points increase as you go down the group, (increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces
How does the reactivity of the halogens change in the group?
Reactivity decreases as you go down the group. (outer electron is further away from protons in nucleus so force is less so cannot gain as easily)
What is a halogen displacement reaction?
Occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
What happens if you add a chlorine solution to a colourless potassium bromide solution?
A displacement reaction occurs. Because chlorine is more reactive than bromine, chlorine DISPLACES bromine from the aqueous solution of the metal halide. The solution becomes orange as bromine is formed.
Chlorine + Potassium Bromide –> Potassium Chloride + bromine
How do the halogens react?
- Some react with metals to form IONIC COMPOUNDS which are METAL HALIDE SALTS
- Some react with non-metals to form simple molecular covalent structures, eg. HCl
What are the typical properties of transition metals?
- Hard, Strong
- Good conductors of heat / electricity
- High density
- High melting points
- Different charges
How can transition metals be useful?
As CATALYSTS, where they speed up the rate of reaction
eg. Iron, which is used in the Haber Process
Some, such as titanium, are good for medical uses such as surgical applications, eg. Hip Replacements
Why does the boiling point of group 1 metals decrease as you go down the group?
Because the negative outer electrons have a weaker force of attraction to the positive nucleus, so are easier to overcome
