Atomic Structure Flashcards
Approx. How many elements are in the periodic table
100
What is a compound
2 or more elements that are chemically combined
What is an element
A substance with only one type of atom
Do compounds share the same properties as the elements they’re made up of?
No
What is a mixture ?
Two or more elements athat are not chemically combined
Do mixtures share the same properties as the elements they’re made up of?
Yes
What are the methods through
which mixtures can be separated (5) and do these involve
chemical reactions?
Filtration
Crystallisation
Simple distillation
Fractional distillation
Chromatography
They do not involve chemical reactions
Describe and explain simple distillation.
Simple distillation is used to separate liquid from a solution – the liquid boils off and condenses in the condenser.
The thermometer will read the boiling point of the pure liquid.
Contrary to evaporation, we get to keep the liquid.
Describe and explain crystallisation/evaporation
Evaporation is a technique for separation of a solid from a solvent (e.g. salt from H2O).
The solution is heated until all the solvent evaporates; the solids stays in the vessel.
Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved).
Then, we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures.
The crystals can be collected and separated from the solvent via filtration.
Describe and explain fractional distillation
Fractional distillation is a technique for separation of a mixture of liquids.
It works when liquids have different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.
The fractionating column contains glass beads. It helps to separate the compounds.
In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the
column.
Describe and explain filtration
Filtration is used to separate an insoluble solid is suspended in a liquid.
The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper.
The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel
Describe and explain chromatography
Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent.
The bottom of the paper has to be in contact with the solvent.
The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
Give the orders of the different versions of the atom model (5)
John Dalton - all matter was made of atoms
JJ Thompson - plum pudding model
Ernest Rutherford - nuclear model I
Neils Bohr - planetary model
James Chadwick - discovery of neutrons
Describe the plum-pudding model,
And who created it?
The atom is a ball of positive charge with negative electron embedded in
it.
Describe Bohr’s planetary model and how it came about
The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) – it came about from the alpha scattering experiments
What did the work of James Chadwick provide evidence for?
The existence of neutrons in the nucleus
State the relative masses and relative charges of the proton, neutron and electron
Masses: 1, 1, very small
Charges: 1, 0 , -1
What is the radius of am atom
1 nanometer
What is the mass number?
The total number of protons and neutrons
What is an isotope?
Atoms of the same element (same proton number) that have a different
number of neutrons.
Do isotopes of a certain
element have the same chemical properties?
They have the same chemical properties as they have the same
electronic structure
What is the relative atomic mass?
The average mass value which takes the mass and abundance of isotopes of an element into account
What are ions
Charged particles (formed when elements lose or gain electrons)
Compare the following properties of metals and non-metals:
MP/BP
Conductivity
Appearance
Malleability
Density
Oxides it forms
Metals:
High
Heat and electricity
Shiny
Yes
High
Basic
Non-metals:
Low
No (except graphite)
Dull
Brittle
Low
Acidic
What is formed when a metal reacts with a non-metal?
An ionic compound
What is formed when a non-metal reacts with a non-metal?
A covalent bond
Atoms share electrons, as opposed to transferring electrons between
each other
Explain the following:
Solute
Solvent
Solution
Miscible
Immiscible
Soluble
Insoluble
A solute is a substance that is dissolved in a solvent. Together, they form a solution.
Miscible refers to the substances (particularly liquids) that mix together, e.g. water and alcohol. Water and oil are immiscible, i.e. they do not mix.
Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in water. Insoluble substance won’t dissolve in a particular solvent.
Are elements in the same group similar or different?
They may have similar chemical properties, as they have the same
number of outer shell electrons.
Early periodic tables were incomplete and elements were placed in inappropriate groups if what was to be followed?
The order of atomic weights
Knowledge of what made it possible to explain why the order based on atomic weights was not always correct?
Isotopes
Mendeleev overcame some problems with the table by doing what? He also changed the order of some elements based on what?
Leaving gaps
Atomic weights
State four characteristics of the Alkali Metals
All have one electron in their outer shell;
have low density;
are stored under oil (to prevent reactions with oxygen or water);
are soft (can be cut with knife).
How do Group 1 elements react with non-metals? Why are these reactions similar for the different Group 1 elements?
They form ionic compounds which are soluble white solids which form colourless solutions – they all have one electron in their outer shell
How do Group 1 elements react with water?
They release hydrogen and form hydroxides which dissolve to form alkaline solutions; react vigorously with water fizzing and moving around on the surface of the water.
How does reactivity change moving down Group 1? Why?
Reactivity increases as the atoms get larger and the distance between the nucleus and the outer electrons increases and thus attraction from the nucleus decreases, allowing them to more easily lose electrons.
State five characteristics of Group 7
- 7 electrons in outer shell
- Coloured vapours
- Diatomic molecules
- Form ionic salts with metals
- Form molecular compounds with non-metals
State five Group 7 elements and states of matter of molecules they form
- Fluorine, F. F2 is a pale yellow gas.
- Chlorine, Cl. Cl2 is a pale green gas.
- Bromine, Br. Br2 is dark brown liquid
- Iodine, I. I2 is a grey solid.
State three changes that occur in Group 7 as one moves down the group
- Higher relative molecular mass (larger and heavier particles)
- Higher melting and boiling point
- Less reactive – less easily gain electrons
Explain how reactivity changes throughout group 7
Reactivity decreases down the group. As we go down the group, the atoms get larger, so an incoming electron will be less tightly held by the attractive forces from the nucleus. That’s why Cl2 displaces Br– and I–
Compare group 1 metals with transition metals
Group 1 metals and transition metals are heat and electricity conductors.
They are shiny when polished and form ionic compounds with non metals.
Transition metals have higher densities and higher melting points than Group 1 metals. They are less reactive and harder than Group 1 metals
State three common characteristics of transition metals
- Ions with different charges
- Coloured compounds
- Catalytic properties
What is a catalyst?
A catalyst is a chemical substance that increases the rate of a
chemical reaction.
It is not used up over the course of the reaction.
State the colours of flames observed when lithium, sodium, and potassium burn in oxygen
Crimson-red, Li
Yellow-orange, Na
Lilac, K
Describe the properties of noble gases. Discuss the trends in properties down the group.
Non-metals, gases, low boiling points, unreactive (full outer shell; they
don’t easily accept or lose electrons).
The boiling point increases down the group, as the atoms get heavier.
