C1 - The Periodic Table Flashcards
All substances are made of atoms. What is an atom?
An atom is the smallest part of an element that can exist
There are about ____ different elements
100
How are compounds formed?
Compounds are formed from elements by chemical reactions
State two features of chemical reactions
Always involve the formation of 1 or more new substances
Often involve a detectable energy change
What are compounds?
Compounds are two or more elements chemically combined in fixed proportions
What is a mixture?
A mixture consists of two or more elements or compounds NOT chemically combined together
The chemical properties of each substance in the mixture are unchanged
What physical processes can mixtures be separated by?
Filtration
Crystallisation
Simple distillation
Fractional distillation
Chromatography
Physical processes do not involve chemical reactions and no new substances are made!
Before the discovery of the electron, what were atoms thought to be?
Tiny spheres that could not be divided
What did the discovery of the electron lead to?
The plum pudding model of the atom. It suggested that the atom is a ball of positive charge with negative electrons embedded in it
What did the alpha scattering experiment conclude? / Why did the new evidence lead to a change in the atomic model?
Some alpha particles deflected right back, suggesting the Mass of an atom was concentrated at the centre (nucleus)
Some alpha particles deflected at angles, suggesting the nucleus must have positive charge
Most of the alpha particles passed through, suggesting atoms have empty space
This lead to the nuclear model. A key indication of how key experimental evidence can lead to a scientific model being changed or replaced
What did the alpha scattering experiment disprove?
The plum pudding model was replaced for the nuclear model
Describe the alpha scattering experiment
Alpha particles were fired at gold foil as it is thin
Some alpha particles passed through, others deflected and some bounced straight back off the gold foil
How did Niels Bohr adapt the nuclear model/add to it?
Suggested that electrons orbit the nucleus at specific distances.
The theoretical calculations of Bohr agreed with experimental observations
What did later experiments AFTER Niels Bohr lead to?
The idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles having the same amount of positive charge
These particles were called protons
About 20 years after the nucleus became an accepted scientific idea, what did the experimental work of James Chadwick provide evidence for?
The existence of neutrons within the nucleus
What is the relative charge of the particles in atoms?
Proton: +1
Neutron: 0
Electron: -1
Why do atoms have no overall electrical charge?
In an atom, the number of electrons is equal to the number of protons in the nucleus
The number of protons in an atom of an element is…
Its atomic number
Atoms are very small. What is their radius?
About 0.1nm (1 x 10^-10m)
What is the radius of a nucleus?
Less than 1/10,000 of that of the atom (1 x 10^-14m)
What are the relative masses of the particles in an atom?
Proton: 1
Neutron: 1
Electron: Very small
The sum of the protons and neutrons in an atom is…
Its mass number
What are isotopes?
Atoms of the same element that have the same number of protons but different number of neutrons
What is relative atomic mass (Ar)?
Average value that takes account of the abundance of the isotopes of the element
Formula for Ar?
[(Mass no. of isotope 1 x % abundance of isotope) / (the latter for isotope 2)] x 100
Can include 3 isotopes!
How are elements in the periodic table arranged?
Why? (3)
- In order of atomic (proton) number
- Because Elements in the same group have the same number of electrons in their outer shell
- Giving them similar chemical properties
Why is the periodic table named as it is?
Similar properties occur at regular intervals
Before the discovery of protons, neutrons and electrons, how did scientists classify elements?
By arranging them in order of their ATOMIC WEIGHTS
What was the issue with early periodic tables?
Were incomplete
Some atoms were placed in inappropriate groups if the strict order of atomic weights were followed
What does the valence/outer electron of an atom represent?
Its group number
What does the amount of energy levels of an atom represent?
The row/period the element is in
How did Dimitri Mendeleev arrange the periodic table? (4)
Left gaps for undiscovered elements
Predicted the properties of undiscovered elements
Gaps were filled with newly discovered elements
In some places, changed the order based on atomic weights
What explained why ordering elements on atomic weight was not always correct?
Isotopes
Elements that react to form positive ions are…
Metals on the left of the periodic table
Elements that do not form positive ions are…
Non-metals on the right of the periodic table
Where are metals and non-metals found on the periodic table?
Metals: Left, towards the bottom
Non-metals: Right, towards the top
Compare metals and non-metals
Metals are strong and malleable, whereas non-metals are brittle
Metals are good conductors of heat and electricity due to delocalised electrons, whereas non-metals do not generally conduct electricity
Metals have a higher density, whereas non-metals have a lower density
Metals have higher melting point and boiling points, whereas non-metals have lower MP and BPs
Metals react to form positively charged ions, whereas non-metals react to form negatively charged ions
What are elements in group 0 called?
Noble gases
Why are noble gases inert (unreactive)?
They have full outer energy levels (except for Helium) and therefore have a stable arrangement. This means they do not need to gain or loose electrons
Explain why the boiling points of the noble gases increases going down the group (5)
- Boiling point increases
- due to an increase in the number of electrons
- creating a stronger negatively-charged force
- leading to greater intermolecular forces
- that require more energy to overcome
What are elements in group 1 called?
Alkali metals
Explain why reactivity increases going down group 1
Increasing reactivity because distance between outer shell and nucleus increases down the group
So there is a weaker attraction between nucleus and outer shell
So electron is more easily lost
Explain how properties of the elements in Group 1 depend on the outer shell of electrons of the atoms
More outer shells = nucleus is further away from valence electrons
so weaker attraction
so electrons easily lost
Going down group 1, what happens to the MP and BP?
Both decrease
Compounds can only be separated into elements by _______ ________
Chemical reactions
What is filtration used for?
This is all important to know if they give you a 6 mark mixture separation question
Separating insoluble solids from liquids
What is crystallisation used for?
Separating a soluble solid from a liquid
What is simple distillation used for?
Separating a liquid from a solid when we want to KEEP the solid
What is fractional distillation used for?
Separating liquids with different boiling points
What is chromatography used for?
To separate different dyes on ink
How do the FIRST 3 alkali metals react with oxygen, chlorine and water?
(Malle sure you know how to compare them)
Water: vigorous reaction to form hydrogen gas and metal hydroxide
Chlorine: vigorous reaction to form white metal chloride salt
Oxygen: Combustion, vigorous reaction forming a metal oxide
What are three properties of alkali metals?
Soft
Very reactive
Low density
Describe group 7 elements
Non-metals
Form 1- ion
Diatomic elements
Explain why there is a higher melting and boiling point going down group 7
Explain why the reactivity of group 7 decreases going down the group
Distance between outer shell and the nucleus increases going down the group
So weaker attraction between the nucleus and outer shell
So harder to gain an electron
Define displacement in terms of halogens
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salts
Compare group 1 and the transition metals
Alkalis form +1 ions, whereas transition metals from ions of different charges
Alkalis are soft, whereas transition metals are hard
Alkali metals are low density, whereas transition metals are high density
Alkali metals are not useful as catalysts, whereas transition metals are used as catalysts
Alkali metals cannot from coloured compounds, whereas transition metals form coloured compounds
Alkali metals have low melting points, whereas transition elements have high melting points
Alkali metals are very reactive, whereas transition metals are less reactive
What are properties of the compounds Cr, Mn, Fe, Co, Ni and Cu
Chromium (CR) = uses to harden steel and resistant against corrosion
Manganese (Mn) = Improves resistance to corrosion and used to make an alloy of aluminium for drink cans
Iron (Fe) = Used to make steel and very resistant against corrosion and alloyed with carbon to make strong structures
Cobalt (Co) = Hard and resistant to corrosion
Nickel (Ni) = Hard, corrosion, resistant alloys
Copper (Cu) = Unreactive so used for water pipes, malleable and conducts electricity
Suggest how to safely heat a substance and describe one way to ensure all salt is dissolved in water
Heat using a water bath/electric heater
Heat/stir
Describe a method to separate a mixture of salt and sand
Place mixture in a beaker
Add water to the mixture and stir using a glass rod
Filter the mixture using a filter and funnel paper
Dry the residue in a warm oven
Evaporate some of the water from the filtrate using a water bath
Leave the solution to cool for 24hrs to form crystals
Remove and pat the crystals dry
Describe a method to carry out a simple chromatography experiment (6)
- Draw a line in pencil near the bottom of a piece of paper
- Place a small sample of each ink on the pencil line
- Pour a shallow layer of water into a beaker and place the paper in the beaker
- The water should be below the paper line and ink spots
- Place lid on the container and wait for solvent to rise to the top of the paper
- Remove paper from the container
Describe how to separate chalk from potassium chloride
Add water to the mixture to dissolve potassium chloride
Filter the mixture using a funnel and funnel paper
The dissolved potassium chloride will pass through and the chalk residue will remain on top
Describe how a solution can be separated using simple distillation
The solution is boiled in rounded bottomed flask
The solution with the lower boiling point evaporates first and passes through a condenser with cold water
This condenses the gaseous solution into a liquid which is then collected in a beaker
Explain when to use fractional distillation instead of simple distillation
If boiling points are too close together, simple distillation cannot be used
Fractional distillation allows substances with close boiling points to be separated
As it provides a temperature gradient
So only substances with a specific BP can reach the top to be separated off without condensing and running back into the flask
Describe a method for fractional distillation
Describe the nuclear model of the atom
A small positively charged nucleus surrounded by a cloud of negative electrons
Compare the plum pudding model and nuclear model of the atom
Both have area of positive charge
Both have electrons
Both are neutral overall
The plum pudding model does not have a nucleus, whereas the nuclear model does
The plum pudding model does not have protons or neutrons, whereas the nuclear model does
The plum pudding model does not have shells/energy levels surrounding the nucleus, whereas nuclear model does
The nuclear model has most of its mass concentrated in the nucleus, whereas the plum pudding model has the mass spread evenly
Only plum pudding model has electrons arranged randomly in a ball of positive charge
What is the radius of the nucleus in relation to the radius of an atom?
Radius of a nucleus is 1/10,000 of the radius of an atom
Give 3 reasons why Mendeleev put iodine in the same group as chlorine
- Iodine has similar properties to other elements in group 7
- iodine has Similar reactivity to other elements in group 7
(Similar properties occur at regular intervals) - Iodine is a diatomic molecule
Explain why lithium and potassium are all in group 1 of the modern periodic table
- They have similar properties
- They have similar reactivity as they have one electron in outer energy level/shell
(Similar properties occur at regular intervals)
Describe the chemical and physical properties of group 1elements
Physical: soft, low density, low MP
Chemical: very reactive, form 1+ ions and colourLESS compounds
Describe 4 things you would see when sodium is added to water
Fizzing
Floats
Moves on surface
Melts/dissolves
State three observations that can be made during the reaction between magnesium and dilute hydrochloric acid
- Effervescence
- Fizzing
- Gets smaller and disappears
Explain why the reactivity of the elements increases going down group 1 from lithium to rubidium, yet decreases going down group 7 from fluorine to iodine
Distance between outer shell and nucleus increases down both groups
So weaker attraction between nucleus and outer shell
So easier for group 1 elements to lose an electron
Harder for group 7 elements to gain an electron
Give two reasons why the discovery of gallium helped Mendeleev’s periodic table to become accepted (2)
- Correctly predicted the chemical properties of gallium
- Gallium fit in a gap he left for future elements
Which group of elements had not been discovered when Mendeelev’s version of the periodic table was publicised?
Group 0 (noble gases)
Review diatomic molecules
What are the differences between compounds and mixtures?
