P1: Atomic Structure & Periodic Table Flashcards
What is an atom?
The smallest part of an element that can exist.
What is an element?
A substance made of one type of atom only.
What does the group it is in suggest about an element?
The number of electrons it has on its outer shell
What is a compound?
A substance that contains two or more elements that are chemically combined.
What is an ion?
An electrically charged particle that is formed when an atom or molecule gains or loses electrons
What does the law of conservation of mass state?
No atoms are lost or made during a chemical reaction
So the total mass of products = total mass of reactants
What is a pure substance?
A substance that consists of only one element or one compound.
What does a mixture consist of?
Two or more different substances, not chemically joined together.
What is filtration used for?
To separate an insoluble solid from a liquid.
List the equipment needed for filtration.
Funnel, filter paper, beaker.
Explain simply filtration.
A mixture is poured through filter paper that sits in a funnel, and the insoluble solid stays on top of the filter paper while the liquid goes through and falls into the beaker below.
What is crystallisation?
The process of producing crystals from a solution by evaporating the solvent.
State the equipment needed for crystallisation.
Evaporating basin, bunsen burner, (heat mat optional)
What are the products of crystallisation?
Crystals.
Explain simply how crystallisation works.
A solution is placed in an evaporating basin and heated with a Bunsen burner. The liquid in the solution evaporates, while solid particles begin to form in the basin. Finally, all the liquid evaporates, leaving solid crystals behind.
How do you obtain large, regularly shaped crystals from crystallisation?
Use a boiling water bath instead of a Bunsen burner, and stop heating the solution when crystals begin to form around the edge of the basin.
How do you sterilise the crystals after crystallisation?
Either use a warm oven or pat them with filter paper.
What is distillation?
A separation method used to separate a solvent from a solution.
What is distillation most commonly used for?
Producing pure water from seawater.
State the equipment needed for distillation.
Bunsen burner, distilling flask, condenser, thermometer, receiving flask.
Simply explain the process of distillation of saltwater.
Salty water is heated, and travels up the beaker, through the tubes into the condenser. The condenser cools down the water vapour and it drips into a beaker. The water has been condensed into a new beaker, and the salt is left behind.
What is fractional distillation?
Distillation of a mixture of several substances.
State the two ways that fractional distillation can be done.
-By collecting different liquids from different parts of the distillation column (the substance with the lowest boiling point collected at the top).
-By continuing to heat the mixture to increase the temperatures in the column (the substance with the lowest boiling point collected first).
What is paper chromatography used for?
Separating mixtures of soluble substances.
Explain simply how chromatography works.
-Ink is dotted along a pencil line on a piece of paper
-The paper is placed into the water, just enough to ALMOST reach the pencil line. The water spreads up the paper, and some of the dye spreads up the paper too
-The paper has now absorbed the solvent and the dye has spread further up the paper.
What are the two different phases of chromatography?
The stationary phase and the mobile phase.
What causes the dissolved substances to move at different rates through the paper?
Their varying attraction to the paper
What does chromatography produce?
A chromatogram
How many spots does a pure substance produce on the chromatogram?
One.
How can you tell if two substances are the same when reading a chromatogram?
-By seeing if they produce the same number of spots that match in colour.
-By seeing if the spots travel the same distance up the paper.
What is an Rf value?
The measure of how far a component travelled in chromatographic separation.
How do you calculate the Rf value?
Distance travelled by the component over the distance travelled by the solvent.
What does a small Rf value mean in chromatography?
It means the dye is more attracted to the paper, so it spends a greater time distributed in the paper than the solvent.
Who created the Plum Pudding Model of the atom?
JJ Thompson.
What did JJ Thompson discover?
The electron.
Describe the structure of the plum pudding model.
A ball of positive charge with negative electrons embedded in it.
Why did the plum pudding model need to change?
Ernest Rutherford discovered the nucleus with his gold scattering experiment.
What model came after the plum pudding model?
The nuclear model.
What is the name of Ernest Rutherford’s model of the atom?
The nuclear model.
What was the gold scattering experiment?
A beam of alpha particles was directed at a very thin gold leaf suspended in a vacuum to determine the movement of particles and to test the plum pudding model of the atom
What conclusion did Rutherford come to thanks to the gold scattering experiment?
-The atom is mostly empty space
-Like charges repel
-Discovery of the nucleus, the positive charge and mass are concentrated in a tiny volume in the atom.
What were the results of the gold scattering experiment?
Most of the alpha particles passed straight through the foil
A small number were deflected by large angles as they passed through the foil
A very small number came straight back off the foil.
Why did the nuclear model of the atom have to change?
Niels Bohr discovered energy levels in the atom that the electrons orbited in
What came after the nuclear model?
Bohr/Planetary model.
What is the name of Niels Bohr’s atom model?
Bohr/planetary model.
Why did the Bohr model of the atom have to change?
James Chadwick proved the existence of the neutron.
How did Chadwick prove the existence of the neutron?
Performed a version of Rutherford’s gold scattering experiment, using a sheet of beryllium and a paraffin block instead of gold foil.
What is the atomic number?
The number of protons.
What is the mass number?
The number of protons and electrons.
What defines an element?
Its atomic number.
What are isotopes?
Forms of an element that have the same number of protons but a different number of neutrons.
What is an ion?
A charged particle. An atom with a different number of electrons.
How do you find the Ar using two isotopes?
(% of isotope A x mass of isotope A) + (% of isotope B x mass of isotope B) all divided by 100
Who created the modern periodic table?
Mendeleev.
What was different about Mendeleev’s periodic table?
-It had gaps in it
-It showed elements with similar chemical properties limed up in groups
Why did Mendeleev leave gaps in his periodic table?
To leave space for undiscovered elements, and to ensure they could be placed near elements with similar properties to it.
How can you tell if an element is a metal by its electronic structure?
If it forms a positive ion it is a metal.
What are the melting and boiling points of metals like in general?
High.
State some properties of a typical metal when solid.
-Good conductor of electricity and heat
-Shiny
-High density
-Malleable
-Ductile
State some properties of a typical non-metal when solid.
-Poor conductor of electricity and heat
-Dull
-Low density
-Brittle
What is the other name for group 8 elements?
Noble gases.
What are the properties of Group 8 elements?
-Low boiling points
-Extremely unreactive
-Complete outer shell
What is the name of the Group 1 elements?
The alkali metals.
What are the properties of the Group 1 elements?
-Soft
-Relatively low melting points
-Low densities
-More reactive as you go down the group
-React with metal to produce a metal hydroxide and hydrogen
-React more vigorously with water going down the group
When alkali metals and water react what do they produce?
A metal hydroxide and hydrogen
What happens with oxygen and alkali metals at room temperature?
Oxygen reacts with the surface of the metal.
What is the name for the Group 7 elements?
Halogens.
Are elements in group 7 more or less reactive as you go down the group?
Less, so they also have a higher mp and bp
What are transition elements?
A metal that is located between groups 2 and 3 of the periodic table and has coloured compounds
What are the properties of transition elements?
-Form coloured compounds
-Conduct electricity in solid and liquid states
-Shiny when freshly cut
-High mp/bp
-High densities
-Greater strength and hardness
How do transition elements react with oxygen?
Slowly, or not at all.
How do transition elements react with cold water?
Slowly, or not at all.
What is reactivity determined by?
How easily the atom can get a full outer shell.
What determines how reactive an element is? (Two things)
-The stronger/weaker the electrostatic attraction to gain/lose an electron
-The nearer it is to having a full shell.
How does the reactivity of elements change in Group 1?
Reactivity increases going down the group.
How does the reactivity of elements change in Group 7?
Gets less reactive as you go down the group.
What happens to the reactivity of Noble Gases?
Stays the same going down.
Explain why the reactivity of elements changes going down Group 1.
-Outer electron is further away from the nucleus as you go down the group
-So there is less attraction between the nucleus and the outer shell (more shielding from the nucleus)
-So the atom loses the electron more easily
Explain why the reactivity of Group 7 elements decreases going down the group.
-Going down the group the shells become further from the nucleus
-So the nucleus has less attraction for the outer shell (so increased shielding between the nucleus and incoming electron)
-So an electron is gained less easily
What is the name of the thing that reduces attraction between the nucleus and the outer shell?
Electron shielding.
What is the alternate name for the Group 7 elements?
Halogens.
What happens in the reaction between an acid and a metal?
React to make hydrogen, which you will see as bubbles.
How can you tell how reactive the metal is when it is reacting with an acid?
The more reactive the metal, the more vigorous the bubbling (which is the production of hydrogen)
What type of reaction is a displacement reaction?
An exothermic reaction.
Which metals will not react with acids?
Ones that are less reactive than Hydrogen, because they can’t displace it.
The greater the temperature change…
The higher the reactivity of a metal.
What does a high temperature change suggest in a displacement reaction?
There is a big difference in the reactivity of the metals.
The greater the potential difference, the bigger the difference in what?
The bigger the difference in reactivity.
Why did Mendeleev’s periodic table become more widely accepted than previous versions?
Mendeleev had predicted properties of missing elements. The ones that were discovered filled in the gaps Mendeleev had left, and the properties matched Mendeleev’s predictions.
