Atomic Structure And The Periodic Table Flashcards
What is an element, compound and mixture?
Element- a substance made of only one type of atom
Compound- contains two or more different elements chemically bonded together, in a fixed ratio
Mixture- contains two or more elements or compounds not chemically bonded together
Describe What is Meant by a Solvent, Solute and Solution
Solvent- the liquid that something dissolves in.
Solute- the substance that dissolves.
Solution- mixture of the solvent and the solute.
What are the advantages of the particle model?
-Animations can show what happens to particles during changes of state
-Shows properties e.g. liquid more dense than gas
What are the disadvantages of the particle model?
-Simplifies all particles to circles rather than showing the atoms which are present
-Shows atoms as solid particles- most of an atom is empty space
What does filtration separate?
Filtration separates an insoluble solid from a liquid/ solution.
Give a method for filtration.
-One beaker contains a mixture of solid and liquid, the other contains a funnel with filter paper
-The solid and liquid mixture is poured into the filter funnel
-The liquid drips through the filter paper but the solid particles are caught in the filter paper
Why does filtration work?
-Filtration works because the filter paper has tiny holes or pores in it.
-These are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid.
What does crystallisation separate?
Crystallisation separates soluble solids from a solution.
Give a method for crystallisation.
-A solution is placed in an evaporating basin and heated with a Bunsen burner
-Heat the solution to evaporate some of the water so that the solution becomes saturated
-Stop heating when crystals begin to form as this shows that the solution is saturated (no more can dissolve)
-Leave to cool to allow more crystals to form. This is because the solubility of solids decreases as the solution cools so as more water evaporates, more crystals form.
Why is speeding up crystallisation by increasing the heat not a good idea?
Many chemicals can be changed by heating so although we could speed up crystallisation using heat, it risks changing the chemical to something unwanted.
What does simple distillation separate?
Simple distillation separates liquids or gases by their different boiling points.
Describe a Method for Simple Distillation
-Simple distillation works because the dissolved solute has a much higher boiling point than the solvent
-When the solution is heated, the solvent evaporates and the solvent vapour leaves the solution.
-It moves away and is cooled and condensed. It is then collected in a beaker.
-The remaining solution becomes more concentrated as the amount of solvent in it decreases.
What does fractional distillation separate.
Fractional distillation separates different liquids from a mixture of liquids.
Give a method for fractional distillation.
-When the mixture is heated, vapours rise through a column.
-The vapours rise up the column until they reach the temperature of their boiling point.
-At this point, the vapours cool and condense.
-Each liquid is then led away from the column.
Why does fractional distillation work?
Fractional distillation works because the different liquids have different boiling points
What does chromatography separate?
Chromatography separates a mixture (often inks or dyes) based on how soluble the compounds in the chosen solvent are.
Give a method for chromatography.
-Set up the chromatogram by dotting along a pencil line (stationary phase).
-Place dots of the solvent along the penicl line.
-Lower the chromatography paper so that the bottom is in the solvent but the pencil line is above it (mobile phase).
-Allow the solvent to travel up the paper until near the top.
-Draw a line where the solvent reached.
What does a chromatogram show?
Separation by chromatography produces a
chromatogram. A paper chromatogram can be used to distinguish between pure and impure substances:
-A pure substance produces one spot on the chromatogram. An impure substance, or mixture, produces two or more spots.
-The further a spot travels, the more soluble that compound is in that solvent (still on start line means the compound is insoluble in that solvent)
-The further a spot travels may also show that it is more attracted the mobile phase than the stationary phase.
Describe the first atomic model.
-Discovered by John Dalton in 1800
-Atoms were tiny spheres that could not be divided
Describe the plum pudding model of the atom
-Discovered by JJ Thompson in 1897
-Atoms were balls of positive charge with negative electrons inside of it
Describe the nuclear model of the atom
-Discovered by Ernest Rutherford in 1909/ 1910
-Atoms contained negative electrons circling a positive nucleus
Describe the adapted nuclear model of the atom.
Discovered by Niels Bohr in 1913
-Electrons orbit the nucleus at specific distances. They are in shells
-In 1932, James Chadwick Chadwick provided the evidence to show the existence of neutrons.
-This was necessary because isotopes have the same number of protons but with different numbers of neutrons.
Compare the Plum Pudding and Nuclear models of the atom.
Plum Pudding:
-solid ball
-positive charge spread throughout atom
Nuclear:
-mostly empty space
-positive charge in centre
-almost all mass concentrated in nucleus
Both:
-electrons
-neither have neutrons
-both have positive charge
Describe the observations and conclusions from the Alpha- scattering experiment.
-Most of the alpha particles passed straight through the gold foil. This shows there must be very few collisions with the atom, suggesting that the atom is mostly empty space.
-Some of the alpha particles were deflected. Only positive charges can repel other positive charges.
This shows that the nucleus of an atom must be positively charged if it repels the positive alpha particle.
-Very few of the alpha particles deflected straight back towards the source. Only particles which hit the nucleus exactly would do this.
-This shows all of the charge of the atom, and therefore all of the mass of the atom must be concentrated into a small area.
Explain why Old Scientific Models are Replaced by New Ones
-New evidence or data is found.
-This evidence cannot be explained by an existing model. This data does not match the predictions made using an existing model.
-The new model explains the new evidence. Data gathered may also match predictions made using the new model.
-For example, the nuclear model of the atom replaced the plum pudding model of the atom.
What is the size of the atom and nucleus.
Atom= 0.1nm (1x10 to the power of -10)
Nucleus= 10 to the power of -14m (1/1000 size of atom)
What is the relative charge of protons, neutrons and electrons?
Proton- +1
Neutron- 0
Electron- -1
What is the relative mass of protons, neutrons and electrons?
Proton- 1
Neutron- 1
Electron- almost zero (1/ 2000)
What is the location of protons, neutrons and electrons in the atom?
Proton- nucleus
Neutron- nucleus
Electron- on the electron shell
Explain why atoms have no overall charge.
-There are an equal number of electrons and protons in an atom so their charges cancel each other out.
-There are also neutrons in an atom but theses have no charge so the atoms’ overall charge remains at zero
State how you would calculate the number of neutrons in an atom
Number of neutron= Mass number- Atomic number
(Big number - Little number)
Describe what is Meant by an Isotope
-Isotopes are atoms of an element with the same number of protons but a different number of neutrons
-Isotopes have the same chemical properties but may have slightly different physical properties because of the different mass to the stable atom
What is meant by Relative Atomic Mass?
The relative atomic mass is an average of the masses of each isotope, taking into account the abundance of each isotope (how common the isotope is)
What is the calculation for relative atomic mass?
Ar= (mass number isotope 1 x percent abundance isotope 1) + (mass number isotope 2 x percent abundance isotope 2) / 100
What is meant by Relative Formula Mass (Mr)?
The Relative Formula mass of a compound is the sum of the relative atomic masses of the atoms in the compound
How is the percentage of an element in a compound calculated?
Percentage of an element in a compound = relative atomic mass of the element x number of atoms of that element/ relative formula mass of the compound
How do features of electronic structure link to the periodic table?
Number of shell = period number
Number of electrons in outermost shell = group number
Number of electrons = atomic number
What is needed for a stable electronic structure.
To have a stable electronic structure, the atom needs to have a full outer shell e.g. the Noble Gases
What is an ion?
An ion is an atom or molecule that has lost or gained electron(s) to form a stable electronic structure.
What type of ion do metals form?
Metallic elements lose electrons and form positive ions . The ion formed has a full outer shell so is stable.
e.g. Group 1- +1
Group 2- +2
Group 3- +3
What type of ion do non-metals form?
Non-metallic elements gain electrons and form negative ions. The ion formed has a full outer shell so is stable.
e.g. Group 7- -1
Group 6- -2
What was the first event in the development of the Periodic Table?
1803- John Dalton- list of elements in order of atomic weight
What was the second event in the development of the Periodic Table?
1865- John Newlands- law of octaves (every 8th element in order of atomic weight had similar properties)
-However this only worked up to calcium
What was the third event in the development of the Periodic Table?
1869- Mendeleev
-assumed more elements were yet to be discovered
-left gaps for future elements with similar properties
–predicted properties of elements yet to be discovered
What was the fourth event in the development of the Periodic Table?
1870 onwards- more elements discovered which matched Mendeleev’s predicted properties. This allowed scientists to fill gaps left in Mendeleev’s table
What was the fifth event in the development of the Periodic Table?
1934- Chadwick- knowledge of isotopes explained why the atomic weight order was inconsistent
How is the modern periodic table organised?
-In order of increasing atomic number
-Some groups have similar properties because the elements have the same number of electrons in their outer shell
How was Mendeleev’s periodic table organised?
-In order of increasing atomic weight
-Some boxes had two elements
-Left gaps for future elements
-Some elements were in a reverse order
Explain why Mendeleev swapped around Iodine and Tellurium.
Iodine was swapped with Tellurium because iodine reacts in a similar way to Fluorine, Chlorine and Bromine so Iodine belongs in the same group.
Explain why Mendeleev left gaps in his Periodic Table.
-Mendeleev left gaps in his table for elements not known at the time.
-By looking at the properties of the elements next to a gap, he could also predict the properties of these undiscovered elements.
Explain why Mendeleev’s predictions led to scientists accepting his Periodic Table.
-Mendeleev’s predictions were extremely close to the properties of elements discovered later on.
-This helped scientists to accept that Mendeleev’s Periodic Table was scientifically valid.
Explain two ways in which the modern periodic table is different from Mendeleev’s.
-The modern periodic table is ordered by increasing atomic number whereas Mendeleev’s was ordered by atomic weight.
-This is because when Mendeleev produced his periodic table atomic structure was not understood
-In the modern periodic table, we have the Noble Gases. These had not been fully discovered when Mendeleev produced his periodic table.
-This is because most elements are discovered because they react with other elements however the Noble Gases are so unreactive, they took a long time to be discovered
Why was Mendeleev ordering his periodic table by atomic weight a problem?
In the modern periodic table, the elements were arranged by the atomic number. However, during Mendeleev’s time, protons had not been discovered so he ordered elements by atomic weight.
The problem is that most elements have isotopes which means that the atomic weight does not always go up in the same order as atomic number.
This meant some elements were initially placed in the wrong group. Mendeleev solved this by switching elements around.
Where are metals and non-metals found on the periodic table?
Metals- found on the left
Non-metals- found on the right (past the BAt line)
List the properties of metals.
-High melting and boiling points
-Good conductor of electricity
-Good conductor of heat
-Shiny (when cut)
-High density
-Malleable
-Ductile
List the properties of non-metals.
-Low melting and boiling points
-Poor conductor of electricity
-Poor conductor of heat
-Dull
-Low density
-Brittle
Why do the Noble Gases not react with other elements.
The Noble Gases do not react with other elements as they already have a full outer shell of electrons.
Explain why the Group 0 elements are gases at room temperature.
All of the Noble Gases have boiling points below 20 degrees Celsius so they are all gases at room temperature.
Describe the link between the relative atomic mass and the boiling point of the Noble Gases.
As the relative atomic mass increases, the boiling point increases.
List the physical properties of the Alkali metals.
-Soft (can be cut with a knife)
-Low densities
-Relatively low melting points
Describe the link between the relative atomic mass and the melting point of the Alkali metals,
As the relative atomic mass increases, the melting point decreases.
Why do the Alkali metals have similar chemical properties?
Atoms of group 1 elements all have one electron in their outer shell. This means that the alkali metals all have similar chemical properties
What is produced when the Alkali metals react with water?
The alkali metals react with water to produce a metal hydroxide and hydrogen.
A hydroxide is alkaline. It is a base that dissolves in water to form an alkaline solution. This solution has a pH greater than 7 and turns universal indicator solution blue or purple.
This is why Group 1 elements are known as Alkali metals.
Describe the Observations when the Alkali Metals React with Water?
Lithium- fizzes steadily; floats; slowly becomes smaller until it disappears
Sodium- fizzes rapidly; floats; melts to form a ball; quickly becomes smaller until it disappears
Potassium- burns violently with sparks and a lilac flame; floats; quickly melts to form a ball; disappears rapidly, often with a small explosion
What is produced when the Alkali metals react with oxygen?
The group 1 elements react with oxygen from the air to make metal oxide
At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.
What observations can be made when the Alkali metals react with oxygen?
The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.
The reactivity of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.
Explain why Group 1 elements are stored under oil.
Group 1 elements are stored under oil because they are very reactive with water and oxygen.
Describe the Reaction Between the Alkali Metals and Chlorine?
-The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides.
-At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions.
-The reactions with chlorine get more vigorous going down the group.
Explain the trend in reactivity in Group 1.
When Group 1 elements react, they lose one electron. Moving down Group 1, the reactivity of the elements increases.
This is because the number of electron shells increases so the distance of the outer shell from the nucleus increases.
This means there is less attraction between outer shell electrons and the nucleus so it becomes easier to lose an electron from the outer shell.
Explain why the halogens form diatomic molecules.
Group 7 elements require one more electron to complete their outer shell. Two atoms join and share a pair of electrons. Now both atoms have a full outer electron shell.
Explain the trend in the melting and boiling points of the Group 7 elements
-As you go down Group 7 both the melting and boiling points also increase.
This is because, going down group 7, the molecules become larger.
-Therefore the intermolecular forces become stronger.
-Therefore more energy is needed to overcome these forces
Explain why the Halogens are different states at room temperature.
The boiling points of some of the halogens (Fluorine and Chlorine) are lower than 20 degrees Celsius so they are both gases.
However, some of the elements (Bromine and Iodine) have boiling points higher than 20 degrees Celsius so Bromine is a liquid and Iodine is a solid.
What are the colours of the Group 7 elements?
Fluorine- yellow
Chlorine- pale green
Bromine- brown
Iodine- purple-black
Moving down group 7, the colours become darker.
Why do the Halogens have similar chemical properties?
Atoms of group 7 elements all have seven electrons in their outer shell. This means that the halogens all have similar chemical reactions.
What is produced when the Halogens react with metals?
The halogens react with metals to produce salts. The salts are made up of ions, which are held together by ionic bonds
What observations can be made when the Halogens react with metals e.g. iron?
Fluorine- burns to produce white iron(III) fluoride
Chlorine- burns vigorously to produce orange-brown iron(III) chloride
Bromine- burns quickly to produce red-brown iron(III) bromide
Iodine- reacts slowly in iodine vapour to produce grey iron(II) iodide
Describe the Recations of Halogens with Non-Metals e.g. Hydrogen
The halogens react with non-metals such as hydrogen. When a halogen reacts with hydrogen, the product is a
compound called a hydrogen halide.
The hydrogen halides are gases at room temperature. They dissolve in water to produce acidic solutions
What observations can be made when the Halogens react with non-metals e.g. Hydrogen
Fluorine- explodes at room temperature and in the dark, forming hydrogen fluoride
Chlorine- explodes with a flame or in sunlight, forming hydrogen chloride
Bromine- vigorous reaction when warmed with hydrogen, forming hydrogen bromide
Iodine -very slow reaction when heated strongly, forming some hydrogen iodide
Explain what take place in a displacement reaction.
A more reactive halogen can displace a less reactive halogen from solutions of its salts.
Explain the trend in reactivity in Group 7.
When Group 7 elements react, they gain one electron. Moving down Group 7, the reactivity of the elements decreases.
This is because the number of electron shells increases so the distance of the outer shell from the nucleus increases.
This means there is less attraction between outer shell electrons and the nucleus so it becomes harder to gain an electron.
What are the physical properties of the Transition Metals?
-Higher melting and boiling points than Group 1
-Harder/ stronger than Group 1 more durable)
-Malleable
-Denser than Group 1
-Better conductors of heat and electricity than Group 1
What are the chemical properties of the Transition Metals?
-Less reactive than Group 1
-Some form coloured compounds (Group 1 only form white compounds)
-Good catalysts
-Form ions with different positive charges
Compare the Transition and Alkali metals.
Alkali metals:
-soft
-low melting points
-low density
-react very rapidly (with oxygen, chlorine and water)
-form +1 ions
Transition metals:
-hard
-high melting points
-high density
-react slowly (with oxygen, chlorine and water)
-form a range of differently charged ions
How can we tell if a Transition metal is present in a compound?
Transition metals tend to form compounds which are coloured.
Why are Transition metals useful in chemical reactions.
Transition metals are good catalysts so can be used to speed up reactions.
