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Chemistry- Molecular Bonding Test
Terms in this set (86)
What are the properties of non-metals?
poor heat conductors
poor electricity conductors
What are Lewis Dot diagrams?
are diagrams that show the bonding between atoms of a molecule, and lone pairs of electrons
What is an advantage of Lewis dot diagrams?
Showing the electrons helps with understanding of how bonds form between atoms.
What is a disadvantage of Lewis dot diagrams?
Provides no information about the length or direction of bonds, or the 3-D shape of molecules.
What are Structural formulas?
are graphic representations of molecular structures, which show how the atoms are arranged
What is an advantage of Structural formulas?
they explain the properties and structure of the compound (which empirical and molecular formulas cannot always represent.)
What is a disadvantage of Structural formulas?
Doesn't contain information on a molecule's three dimensional structure.
What are ball and stick models?
display the three-dimensional position of the atoms and the bonds between them.
The atoms are typically represented by spheres, connected by rods which represent the bonds.
What is an advantage of ball and stick models?
Shows the three-dimensional arrangement of atoms and bonds.
What is a disadvantage of ball and stick models?
Different atoms may have different sizes and bond lengths may not be in proportion.
What are space filling models?
represents the size and shape of a molecule, showing how much space each atom occupies.
What is an advantage of space filling models?
Shows three-dimensional arrangement as well as size relationships between atoms more accurately.
What is a disadvantage of space filling models?
Bonds are not visible so it is difficult to see the internal structure.
State some general rules about Electronegativity.
- Non-metals are more electronegative than metals
- Electronegativity increases from left to right across a period
- Electronegativity decreases going down a group
- Flourine is the most electronegative element
What is Covalent bonding?
Is the sharing of valence electrons between 2 or more non-metal atoms.
In a Covalent bond, would you expect the shared electrons to be shared equally?
No, the electrons would not be shared equally unless the bond was identical atoms
E.g. between two hydrogen atoms
Why are hydrogen atoms unstable?
They do not have a full valence shell of electrons
What happens when 2 hydrogen atoms react?
The two valence electrons are shared by both atoms to become stable, which forms a molecule of Hydrogen Gas.
Structural formula: H-H
What is a Molecule?
A group of atoms bonded together
What are Intramolecular bonds?
Bonds that form between atoms within a molecule
What are the three types of Intramolecular bonding?
Metallic bonding, Ionic Bonding and Covalent Bonding
What is an example of an Intramolecular bond?
The H and O bonding in H2O
What are Intermolecular bonds?
Bonds between molecules
What are the three types of Intermolecular bonding?
- Dipole- Dipole Interaction
- Hydrogen Bonding (strong)
- Dispersion Forces (weak)
What are Lone pairs?
Are pairs of electrons that are not involved in bonding
Why do lone pairs repel more than bonding pairs?
Like charges repel, and therefore want to be as far apart from eachother as possible.
Why are lone pairs of electrons important even though they have not taken part in the chemical reaction?
Lone pairs can affect the shape of a molecule
E.g. Two lone pairs in a water molecule make it V-shaped/bent
What is a diatomic molecule?
One type of atom that will bond with itself to share electrons to have a full valence level.
What are some examples of Diatomic molecules?
Oxygen Gas - O2
Nitrogen Gas - N2
Hydrogen Gas - H2
What is the shape of all Diatomic Molecules?
What does the shape of a molecule describe?
describes the way in which the atoms are arranged.
When are molecules most stable?
when the electron pairs (both bonding and non-bonding) are as far apart as possible.
What are the 4 most common shapes of molecules?
- Bent or V-shaped
- Triangular pyramid
What is a Linear molecule? (shape)
Two groups form a straight line (linear) with 180 degrees between them.
What is an exmaple of a linear molecule?
- Carbon Dioxide
- Hydrogen Flouride
What is a bent/v-shaped molecule?
Three groups will form a flat triangle (triagonal planar) that are all angled at 120 degrees.
What is an example of a Bent/ V-shaped molecule?
- Water - Nitrogen Dioxide - Sulfur dichloride
What is a Tetrahedral molecule?
Four groups will form a Tetrahedron, which are all angled at 109.5 degrees.
What is an example of a Tetrahedral molecule?
- Methane (CH4)
What is an Octahedral molecule?
Six groups surrounding a central atom will form an octahedron which are either angled at 90 or 180 degrees.
What is an example of an Octahedral molecule?
What is the VSEPR model/theory?
Is a model used to predict and explain the three-dimensional shape due to the negatively charged electrons in pairs which repel from eachother, and try to get as far away from eachother as possible. (electrostatic repulsion)
What is Polarity?
When there is a significant difference in electronegativity between 2 non-metal atoms that are covalently bonded.
What occurs in a Polarised bond?
The pair of shared electrons spend more time closer to the more electronegative element.
What are some examples of Polar molecules?
- Hydrochloric acid
What is a Dipole-Dipole interaction?
are attractive forces between the positive end of one polar molecule, and the negative end of another polar molecule.
What two conditions must apply if a molecule is to be a dipole?
It must have polar bonds, and the partial charges must be distributed asymmetrically across the molecule
What are Dispersion forces? (non-polar)
They occur at any given time, when the electrons in an atom or molecule are unevenly distributed, which creates an instantaneous dipole
(There is an attraction between dipoles)
What is an example of Dispersion Forces?
Molecules of Cl2 and Br2 do not have dipoles, but intermolecular forces are strong enough to cause liquid and solid phases to exist.
What is Hydrogen Bonding?
Occurs between molecules that have a hydrogen atom bonded to a more electronegative N, O or F atom.
What is one unsual property of water?
One unusual property of water is that ice floats.
Why does ice float in water?
Ice floats because ice is less dense than liquid
Why is ice less dense than water?
The hydrogen bonding holds the water molecules in ice in a regular crystal lattice. In this lattice, the molecules are held further apart than in liquid water.
What happens to the density of water when ice melts?
the density of the water increases as the crystal lattice collapses, and the water molecules pack together more tightly.
What happens as the temperature of water increases further?
Water molecules in the liquid move and vibrate more rapidly, which causes the molecules to spread further apart.
What happens as the water molecules move further apart?
As the molecules move further apart, the liquid becomes less dense.
What is a 3D covalent lattice?
Is one of the strongest types of bonding between particles in a solid.
What is a characteristic of Covalent bonds in a crystal structure?
Covalent bonds extend in all directions in the crystal structure.
What are three examples of a Giant covalent structure?
What is the arrangement of Diamond?
Diamond is composed of carbon atoms each bonded covalently to 4 other carbon atoms, in a tetrahedral arrangement.
What is an Allotrope?
Are substances which have the same molecular formula but different structures and similar properties
What are is an example of Allotropes?
Diamond and Graphite
Describe the structure of Diamond
Diamond is composed of carbon atoms each bonded covalently to 4 other carbon atoms in a tetrahedral arrangement.
What are some propterties of Diamond?
- High melting point
- Poor conductors of heat and electricity
What is the explanation for Diamond's properties?
The carbon atoms have a regular lattice arrangement which are held by strong covalent bonds, meaning there are no delocalised electrons.
This makes diamonds structure very rigid and hard.
What are some practical/industrial uses of Diamond?
- Cutting utensils
Describe the structure of Silicon Dioxide (SiO2)
Tetrahedral arrangement with one silicon bonded to four oxygen atoms.
Is Silicon Dioxide polar or non polar?
What are the properties of Silicon Dioxide?
- High melting/ boiling point
- Poor conductor
Describe the structure of Graphite.
Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom also has one delocalised electron.
Describe the bonding between the layers of Graphite.
The layers are held by dispersion forces, which causes the layers to easily slide over eachother. (very weak bonds)
Why does Graphite have delocalised electrons?
The double bonds form a circular pattern as it relocates around the 6-membered ring, which causes one of the bonding electrons to move freely along the layers.
What are the properties of Graphite?
- Conducts heat and electricity
- High melting/boiling point
What are practical/industrial uses of Graphite?
What are the properties of Nanomaterials?
Nanomaterials have a very high surface area to volume ratio, which gives them some unique or enhanced properties.
What are Fullerenes?
Are roughly spherical group of carbon atoms arranged in series of pentagons and hexagons (similar to the shape of a soccer ball)
Describe the structure of a Fullerene.
Are composed of stacked graphene sheets of linked hexagonal rings. (similar to the structure of graphene)
What do Fullerenes consist of?
Consist of 60 or more carbon atoms arranged like a hollow sphere and held together by strong covalent bonds.
What are the properties of Fullerene?
- Can act as electrical conductors or semiconductors
- High tensile strength
- High ductility
- Very strong and can resist pressure
What are the practical/industrial uses of Fullerenes?
- Drug dellivery systems
What is Graphene?
A sheet of carbon atoms joined together in hexagons (a single layer of graphite)
What are the properties of Graphene?
- Good conductor of electricity
- Extremely strong
What are the uses of Graphene?
- Layered onto other materials which are usually not good conductors
- Can be manufactured as tubes or other 3-D structures.
What is the structure of Nanotubes?
Consists of a hollow cylindrical tube made of a sheet of graphite.
What are the properties of nanotubes?
- High tensile strength
- Good conductors or semiconductors
- Toxic when inhaled
- Can contain chemicals (metals, proteins, oxides)
What are the applications of Nanotubes?
- Touch screen devices
- Solar panels
- Removing pollution from water
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