End Of Year Exams Flashcards
How did Dmitri Mendeleev create his periodic table?
- Mendeleev arranged the elements in order of increasing relative atomic mass.
- Then, he arranged the elements by putting those with similar properties below each other into groups
- He left gaps for yet to be discovered elements
How was the modern periodic table created?
- After the discovery of protons, scientists realised that the atomic number of an element is the same as the number of protons in its nucleus.
- In the modern periodic table, the elements are arranged according to their atomic number - not their relative atomic mass.
- Rows, called periods, in order of increasing atomic number
- Vertical columns, called groups, where the elements have similar properties
How does the electronic configuration of an element relate to its position on the periodic table?
- The number of shells in the electronic configuration of an element is represented in the periodic table as the period number that element is situated in
- The number of electrons in the outermost shell of an element is represented in the periodic table as the group number that element is situated in
- The number of electrons in all shells of an element is represented in the periodic table as the element’s atomic number
What does the electronic configuration of sodium (2.8.1) show?
It is in:
- Period 3
- Group 1
- Has the atomic number of 11
What is the link between the electronic configuration of an element and its properties?
When atoms collide and react, it is the outer electrons that meet and interact. So, elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.
Describe Dalton’s model’s features
- atoms cannot be broken down into anything simpler
- the atoms of a given element are identical to each other
- the atoms of different elements are different from one another
- during chemical reactions atoms rearrange to make different substances
How does today’s model of atomic structure differ from Dalton’s model
- atoms can be broken down into three smaller particles: protons, neutrons and electrons
- atoms of an element have identical numbers of protons and electrons, but can have different numbers of neutrons
- atoms of different elements have different numbers of protons and electrons
Describe atomic structure
An atom has a central nucleus surrounded by electrons arranged in areas called shells.
What are the relative charges of protons, electrons and neutrons
Proton: +1
Electron: -1
Neutron: 0
What are the relative masses of protons, electrons and neutrons
Proton: 1
Electron: 1/1835
Neutron: 1
What is an isotope?
Atoms of an element that have the same number of protons and electrons, but different numbers of neutrons in their nuclei are called isotopes.
What is an ion
An ion is an atom or group of atoms with a positive or negative charge. Ions form when atoms lose or gain electrons to obtain a full outer shell.
How is an ion made
- Metal atoms lose electrons, so they have more protons than electrons to become positively charged ions (cations)
- Non-metal atoms gain electrons, so they have more electrons than protons to become negatively charged (anions)
What is a covalent bond
When atoms share electrons on their outer shell in order to gain a full outer shell
This occurs between non metals
What is a metallic bond
This occurs between metals
Metallic bonding is the attraction between the positive ions in a regular lattice and the delocalised electrons. Delocalised electrons are free to move throughout the whole structure.
What phases does chromatography rely on
Chromatography relies on two different ‘phases’:
- the stationary phase, which in paper chromatography is very uniform, absorbent paper
- the mobile phase is the solvent that moves through the paper, carrying different substances with it
Why do some substances move faster through chromatography paper
The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper.
Why is a chromatogram used
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
A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if:
- they produce the same number of spots, and these match in colour
- the spots travel the same distance up the paper
What are the structures of each chemical bond?
Ionic: Giant ionic lattice
Covalent: Simple covalent, giant covalent
Metallic: Giant metallic lattice
Describe the structure of a giant ionic lattice
An ionic compound is a giant structure of ions. The ions have a regular, repeating arrangement called an ionic lattice.
The lattice is formed because the ions attract each other and form a regular pattern with oppositely charged ions next to each other.
An ionic lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions. The forces act in all directions in the lattice.
What are the properties of an ionic compound?
- Crystalline solids
- Can be dissolved or molten
- Hard and brittle
- Can only conduct electricity when dissolved or molten
- High melting and boiling points
Why are ionic compounds crystalline?
Because of the strong electrostatic interaction between these oppositely charged ions, ionic compounds form rigid crystals.
Why do ionic compounds have high melting and boiling points?
The ionic compounds are usually hard because the ions are held by strong force of attraction as the positive and negative ions are strongly attracted to each other and difficult to separate.
Why can ionic compounds only conduct electricity when molten or dissolved?
Ionic compounds conduct electricity when molten, because their ions are free to move from place to place.
Ionic compounds cannot conduct electricity when solid, as their ions are held in fixed positions and cannot move.
What is the difference between giant covalent and simple covalent compounds?
The key difference is that simple covalent molecules have a small and fixed number of atoms, while giant structures have large and variable numbers of atoms.
Describe the structure of simple covalent bond
There are strong covalent bonds between atoms that form molecules together. However, there are weak intermolecular forces between the molecules.
What are the properties of a simple covalent substance
- Cannot conduct electricity
- Low melting and boiling points
- Don’t dissolve in water
Why can’t simple molecules conduct electricity?
The molecules have a neutral charge so they can’t conduct electricity and there are no electrons that are free to move
Why do simple molecules have low melting and boiling points?
They have relatively low melting points and low boiling points because the molecules are held together by weak intermolecular forces that break down easily.
What are the properties of giant covalent structures?
- High melting and boiling points
- Most compounds don’t conduct electricity however some do.
What is an allotrope?
Allotropes are different forms of the same element, in the same state.
Describe the structure of diamond
- Giant covalent structure
- Each carbon atom is bonded to 4 other carbon atoms
- Has a tetrahedral 3D structure
What are the properties of diamond and what are its uses
- High melting and boiling points
- Doesn’t conduct electricity
- Hard
- Used to cut through metals, rocks and glass
Describe the structure of graphite
- Each carbon atom forms three covalent bonds with 3 other atoms
- Forms layers of hexagonal rings
- Weak forces of attraction between layers
- There is one delocalised electron for each atom
What are the properties of graphite and its uses
- High melting and boiling points
- Good electrical conductivity
- Soft
- Lubricant
- Pencils
What are the properties of graphene
- High melting and boiling points
- Good electrical conductivity
- Very strong
What is the structure of a giant metallic lattice?
Metals are giant lattices of positive ions arranged in regular layers, with delocalised electrons free to move throughout the structure.
What are the properties of giant metallic structures?
- High melting and boiling points
- Good electrical conductivity
- Malleable and ductile
Why do giant metallic substances have high melting and boiling points?
High temperatures are required to break strong metallic bonds.
Why do giant metallic substances have good electrical conductivity?
Metal’s delocalised electrons can move and carry charge.
Why are giant metallic substances malleable and ductile?
Metal’s layers of ions can slide over each other, but are still held together by the delocalised electrons. This means metal is malleable (it can be hammered into shape) and ductile (it can be drawn out into wires)
