Chemistry Atomic structure, Covalent bonding and Metallic bonding half term test Flashcards
What’s the order of the development of the atomic models?
- Greeks said that atoms are tiny spheres that cannot be divided
- Plum pudding model, a ball of positive charge with electrons embedded in it
- Alpha particle scattering experiment, showed that the mass of an atom is concentrated at the centre and the nucleus is charged
- Positively charged nucleus orbited by electrons like planets around the sun
- Niels Bohr adopted the nuclear model by suggesting that the electrons orbit at specific distances
Definition of atom
Smallest part of an element that can exist
Definition of element
Contains only one type of atom
Definition of compound
consists of two or more elements or compounds that are chemically combined
How to calculate relative atomic mass
Total mass of atoms/ total number of atoms
What are isotopes?
atoms of the same element but with different numbers of neutrons therefore different masses.
Who discovered the neutron?
James Chadwick
What is covalent bonding?
When atoms share pairs of electrons. (strong bond)
Advantages of displayed formula
- quick and easy to draw and identify
- shows how they are bonded to each other
Advantages of ball and stick models
- shows the shape of the molecule
- 3D
- shows which atoms are bonded to which
Advantages of dot and cross diagrams
- shows which atoms are bonded to each other
- shows electrons
Disadvantages of displayed formula
- 2D
- cannot see electrons
Disadvantages of ball and stick models
- does not show electrons
- hard to draw when there are many atoms
Disadvantages of dot and cross diagrams
- does not show electrons orbiting
- hard to draw if there are many atoms
- 2D
Size of atom
1 nanometer (1x10^-10m)
Size of nucleus
About 1x10^-14m
Difference between simple and giant covalent structures
simple covalent structures have a fixed number of atoms (eg. ammonia) and giant covalent structures have large and variable amounts of atoms
Properties of giant covalent structures
- high boiling and melting points (strong intermolecular forces)
- strong (covalent bonds)
- cannot conduct electricity (except for graphite and graphene)
- has a lattice structure
- not soluble in water
Properties of simple covalent molecules
- low boiling and melting points
- weak intermolecular forces
- do not conduct electricity as they do not have an overall electric charge
What are polymers?
large molecules with many small repeating units called monomers that are joined with strong covalent bonds
Definition of mixture
A mixture consists of two or more elements or compounds that are not chemically combined
What is graphene?
A single layer of graphite
Properties of graphene
- very high melting point
- very strong
- conducts electricity well due to having delocalised electrons
- often used in electronics and composites
What are fullerenes?
- Molecules of carbon atoms with hollow shapes
- based on hexagonal rings of carbon atoms but may also contain rings of five or seven carbon atoms
What was the first fullerene that was discovered?
Buckminsterfullerene (C60)
Properties of fullerenes
- low melting and boiling point (weak intermolecular forces
- cage like structure (can transport substances inside it eg. medicine)
- good catalyst (large surface area compared to volume)
- has a delocalised electron that can carry the charge
- lightweight
Are the intermolecular forces of polymers strong
yes, so they remain as solids at room temperature
How is ethene converted to polyethene?
the double covalent bond between the carbon atoms are broken and is joined to a neighboring molecule
Draw the shorthand way of representing a polymer
(see goodnotes)
Compare diamond to graphite
(see goodnotes)
Where do we find metals on the periodic table?
on the left
What is metallic bonding?
- A strong electrostatic force of attraction between positive and delocalised electrons as the delocalised electrons are free to move through (not throughout) the whole structure, leaving positive ions.
Advantages of the 2D diagram of metallic bonding
- can see the “sea” of electrons
- can see every atom easily (none are blocked or covered)
Advantages of the 3D diagram of metallic bonding
- shows layer arrangement of the atoms and the giant lattice structure
Disadvantages of the 2D diagram of metallic bonding
- cannot see the layer arrangement of the atoms/ the giant lattice structure
- doesn’t show each indivual electron
Disadvantages of the 3D diagram of metallic bonding
- doesn’t show electrons at all
- can only see outermost atoms
Properties of metals
- high melting and boiling point: strong electrostatic forces of attraction so it takes a lot of thermal energy to break the bond
- malleable: metals consist of layers of ions that are the same size that can slide over each other when the metal is bent, hammered, or pressed
- electrical conductor: delocalised electrons can carry electrical charge through the metal and move through the structure
Why are alloys stronger and harder than pure metals
- the layers are distorted so the particles cannot slide over each other as well
Why do alloys not conduct as well as pure metals
- distorted layers cause the delocalised electrons to not be able to pass through the structure as easily.
Describe ionic bonding
the metal atom loses its outermost electrons and transfers them to the non metal atom to complete the non metal atom’s outer shell. This makes the metal atom a positive ion and the non metal atom a negative ion as there aren’t enough electrons to balance the charge of the protons and vice versa. there is a strong electrostatic force of attraction between the oppositely charged ions
Properties of ionic compounds
- high melting and boiling point : the lattice structure and the strong electrostatic forces between the ions require a lot of thermal energy to break
- Crystalline : this reflects the regular arrangement of teh ions
- brittle : small distortions in the crystal bring ions with the same charge together and similar charges repel each other, breaking the crystal apart
- soluble in water : the slightly negative oxygen in the water attracts the positive ions while the slightly negative hydrogen in the water attracts negative ions, pulling the crystal apart
- do not conduct when solid : the ions cannot move when the ionic compound is solid there cannot carry any charge and cannot conduct electricity
- conduct when molten/ in solution : the ions are free to move when molten or dissolved and will carry the charge and conduct electricity
Draw a ionic bonding diagram for sodium chloride
see goodnotes
