Chemistry Test 3 Flashcards
How does a covalent bond work? What kind of elements are they? between
Covalent bonds form between non-metal elements. It forms by the mutual sharing of valence electrons between two of such atoms.
What are Lewis structures used to represent?
Covalent and ionic molecules and compounds
How many different types of covalent bonds are there and what are the symbols for them and what do these represent?
Single Bond - two atoms share 2 electrons (Pair)
Double Bond - two atoms share 4 electrons (2 pairs)
Triple Bond - two atoms share 6 electrons (3 pairs)
What is a pair of electrons of a covalent atom in a molecule or compounds that is not in a double bond called?
Lone pair
What is the small symbol for electrons?
e^-
What are substances made of discrete covalent molecules called?
Covalent molecular substances
Examples of discrete covalent molecules
Water (H20)
Oxygen (O2)
Carbon Dioxide (CO2)
What are intramolecular forces? Are they strong or weak?
The intramolecular forces are the bond within these molecules, and they are strong.
What are intermolecular forces? Are they strong or weak?
Intermolecular forces are the forces in-between molecules. These are weak and easy to break
Why do covalent molecular substances usually have low MP and BP and usually gas or liquid at room temp?
The forces that hold the molecules together (intermolecular forces) are weak, and can be overcome with less energy.
Why do covalent molecular substances not conduct energy?
There are no charged particles (electrons or ions) that move through the substance.
Why do covalent molecular substances form soft solids?
The forces that hold the molecules together (intermolecular forces) are weak
Why do covalent molecular substances tend to be malleable instead of shattering?
Because the forces between molecules (intermolecular forces) are weak and so molecules can easily be moved around.
Why do covalent molecular substances have variable solubilities?
Because the solubility depends on the forces between these molecules (intermolecular forces)
Is it common for covalent molecular substances to be solids at room temperature? If so, what are these called?
No, it is not common, these solids are called molecular solids.
What is the molecular solid?
a 3D molecular lattice, held together by weak intermolecular forces of attraction, such as in Iodine
Properties of Molecular Solids
- Low melting and Boiling Points
- Soft and brittle - Shatter when heated
- Cannot conduct electricity
What are covalent network substances? What is their composition and give examples of such substances.
Covalent network substances are substances where the covalent bonds don’t form discrete molecules, but form vast networks of non-metal atoms, bonded together covalently (3D network). Examples of these substances are diamond, sand and graphite. Common elements are boron, carbon and silicon
Why are covalent network substances usually very strong?
The intermolecular forces in covalent network substances are effectively covalent bonds, and so inherently require a great amount of energy to disrupt.
Why covalent network substances have high MP and BP and are usually solids at room temperature.
The covalent bonds that hold the atoms (network) together are very strong.
Why do covalent network substances not conduct electricity?
There are no charged particles such as electrons or ions, free moving in the structure of the substance.
Why are covalent network substances extremely hard and brittle?
Covalent bonds between atoms are very strong, but an impact force disrupts the positions of atoms in the structure and cause the network to shatter.
Why are covalent network substances usually insoluble in water and most solvents?
No attraction between atoms in the network and water molecules. Cannot dissociate.
Allotropes/Allotropes of Carbon - Properties?
Both Diamond and Graphite are made up of Carbon atoms. Allotropes as such are different forms of the same element. Allotropes of Carbon have different properties as the atoms are bonded in different arrangements, which create different network structures.
Properties of Diamond - Covalent Bonding? Physical Properties?
All four valence electrons of the carbon’s valence shell form covalent bonds. This makes diamonds very hard, High MP and BP, and they cannot conduct electricity (no free moving charges particles such as ions or electrons)
Graphite Properties - Covalent Bonding? Physical Properties?
In graphite, only 3 out of 4 valence electrons of each carbon atom are involved in covalent bonding. This makes graphite soft and slippery as layers can easily slide over each other as week forces of attraction are easily broken. Graphite conducts electricity because the 1 free electron from each carbon means that each layer has delocalized electrons which can carry charge.
Fullerenes
Fullerenes are allotropes which consist of carbon atoms atoms bonded together to form an enclosed or partially closed mesh. They are covalent molecular substances.
Buckminster Fullerenes (Bucky Balls)
Type of fullerene. This allotrope of carbon forms a sphere shape. Have 60 carbon atoms, each of which is bonded to three other atoms by two single bonds and one double bond.
Carbon Nanotubes
They are cylindrical carbon-based covalent network substances.
What are these fullerenes used for?
Medicine delivery (pharmaceutical use)
How does ionic bonding work?
Transfer of electrons between metal and nonmetal atoms to reach octet configuration.
How are ionic lattices held together?
Electrostatic attraction between anions and cations in the lattice
Properties of Ionic Substances - Physical properties?
High Melting and Boiling points due to strong electrostatic attraction between ions
Hard and brittle (not malleable) due to strong electrostatic attraction between ions and when impacted, ions of similar charges repel each other, shattering the lattice.
They do not conduct electricity in a solid state as there are no free moving charged particles.
They have varying solubilities.
Good conductors of electricity when dissolved in water or in molten state - free moving charged particles.
Ionic substances dissolving explanation
If the particles in the lattice are more attracted to each other (electrostatic attraction) than to the water molecules, it will not dissolve.
Writing formula for ionic compounds
Empirical ionic formulae rules:
- Switch charges to subscripts (unless cancels out or irrelevant; same charge like 1 and -1)
- Transition metals have variable charges expressed as Roman numerals in brackets e.g (II)
- Polyatomic ions also have charges and are placed in brackets if there is a subscript, these brackets can be expanded to see number of each atom needed to balance compound
Naming ionic compounds
-ide suffix
no prefixes
What is Metallic Bonding, can it conduct electricity?
Regular arrangement of metal atoms with electrostatic forces of attraction between nuclei of these atoms and their delocalized electron. Mobile sea of delocalized electron moves within the 3D lattice. Can conduct electricity due to free moving sea of delocalized electrons.
How do metal atoms achieve stability in metallic bonding?
By offloading valence electrons to attain octet configuration. These electrons prevent newly formed positive ions from repulsing each other due to similar. charges. Metallic ions vibrate about in fixed positions in the lattice.
Metallic Bonding strength factors?
Depends on the number of valences electrons donated to cloud (depends on element) and the size of the atom/ion.
Sodium Metallic Bonding strength
Relatively weak as each ion only donates the one valence electron to the cloud.
Potassium Metallic Bonding strength
Weaker than sodium since the resulting ion is larger and the electron cloud has a bigger volume to cover so less effective at holding the ions together.
Mobile sea of electron + -
Electrons attracted to the positive end are replaced by those entering from the negative end.
Metallic Properties - Bonding? Physical Properties?
Non-directional Bonding
Malleable: Can be hammered into sheets, manipulated
Ductile: Can be drawn out into rods and wires
Can be translucent at times.
Ionic Solidity at room temperature? Reason Trends?
Solids at room temperature: Moderate to high temperature is needed to disrupt the lattice and allow the metal to melt.
Increases from left to right on a period.
Ionic High Melting Point: Reasons, Factors and periodic trends?
Measures of how strong the cloud holds the positive ions.
Depends on:
Electron Density of the cloud
Ionic/atomic size
Melting point increases across a period. Electron cloud density increases due to the number of electrons donated per atom.
Melting Point decreases down a group, because Ionic radius increases down the group.
What is Relative Formula Mass (Mr) + Formula?
Calculated from the sum of all of a molecule or compounds atoms relative atomic masses.
Mr = (no. of element x Ar of element) + same things depending on the number of elements present in the substance
What is Percentage composition + Formula?
The percentage by mass of an element in a compound. Can be used to work out how pure a substance is or identify an unknown substance.
%element = ((Ar of element x number of atoms) / (Mr of compound)) x 100
Molecular Formula vs Empirical Formula
The molecular formula of a compound tells you how many of each type of atom are present in one molecule. e.g. Ethane - C2H6
Empirical formula however gives the simplest whole number ratio of the type of atoms present in one molecule. e.g Ethane
- CH3. Ionic compounds always use empirical formula.
What is the mole (SI) unit used for?
Describing the amount of a substance in terms of the number of particles.
What does Avogadro’s number really represent?
Avogadro’s number represents the number of particles in one mole.
How is molar mass of substances such as water, carbon dioxide, magnesium oxide and sodium hydroxide found?
The molar mass of these substances are found by adding together the molar masses (atomic mass) of the elements in each molecule or formula.
Moles within Moles for 1 mole of NaOH?
1 mole of NaOH contains 1 mole of Na+ ions and 1 mole of OH- ions
Moles within Moles for 1 mole of Al2(SO4)3?
2 moles of Aluminium ions and 3 moles of Sulphate ions
What is Standard Pressure?
Standard pressure is 101.3 kPa
Molar Volume Methods
STP and Non STP
Stoichiometry
We can use the coefficients in a balanced equation as relative number of moles.
How to go from number of moles to number of particles and vice versa.
Number of moles x Avogadro’s constant = number of particles and vice versa. divide
Molar Volume of a Gas at STP formula
n(gas) = V/22.71 mol
What is non-STP
Not at STP requirements
Molar Volume of a Gas at Non STP formula
n(gas) = P x V/ R (universal constant) x T mol
