Chapter 5 - Chemical Bonding Flashcards
Compound
Substance made up of two or more different elements combined together chemically
Octet rule
When bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost energy level
What are some exceptions to the octet rule?
Transition metals don’t always need eight in the outer shell
Elements near helium in the periodic table tend to only have two in the outer shell
Ion
Charged atom or group of atoms which formed either by losing or gaining electrons
Anion
negative ion
has gained electron
cation
positive ion
has lost electron
Ionic bond
Force of attraction between oppositely charged ions in a compound. Ionic bonds are always formed by the complete transfer of electrons from one atom to another
The 3D arrangement of ions is called a …
… crystal lattice
Give examples of uses of ionic compounds
Athletes take salt tablets to replace the salt lost by sweating Washing soda (Na₂CO₃) is used to soften water
Valency
The number of hydrogen atoms (or any other monovalent element) with which each atom of the element combines
What are the valencies of iron?
Fe⁺²
Fe⁺³
What are the valencies of copper?
Cu⁺
Cu⁺²
What are the valencies of chromium?
Cr⁺³
Cr⁺⁶
What are the valencies of manganese?
Mn⁺²
Mn⁺⁴
Mn⁺⁷
Why do some transition metals have variable valencies?
There is such a small energy difference between 4s and 3d sublevels
What characteristics do transition elements typically show that scandium and zinc don’t?
Variable valency
Transition elements usually form coloured compounds
Transition elements are used as catalysts
Transition metal
One that forms at least one ion with a partially filled d sublevel
Molecule
Group of atoms joined together. It is the smallest particle of an element or compound that can exist independently
Sigma bond
Formed by the head on overlap of two s or p orbitals
Pi bond
Formed by the sideways overlap of p orbitals
Which is stronger: sigma or pi bond?
Sigma as there is an orbital overlap
What are the characteristics of ionic bonds?
Hard and brittle
High melting and boiling points
Solid at room temperature
Conduct electricity in molten state or dissolved in water
What are the characteristics of covalent bonds?
Usually soft
Low melting and boiling point
Liquids, gases or soft solids at room temperature
Do not conduct electricity
What does the VSEPR in VSEPR theory stand for?
Valence Shell Electron Pair Repulsion theory
Bond pair
Pair of electrons that make up a covalent bond
Lone pair
Other electrons present that are not involved in bonding
Order the amount of repulsion between pairs of electrons in an atom
lone pair/lone pair > lone pair/bond pair > bond pair/bond pair
What shape is this molecule? 2 bond pairs, 0 lone pairs. What size are the angles formed?
linear
180°
What shape is this molecule? 3 bond pairs, 0 lone pairs. What size are the angles formed?
triangular planar
120°
What shape is this molecule? 4 bond pairs, 0 lone pairs. What size are the angles formed?
tetrahedral
109.5°
What shape is this molecule? 3 bond pairs, 1 lone pairs. What size are the angles formed?
pyramidal
107°
What shape is this molecule? 2 bond pairs, 2 lone pairs. What size are the angles formed?
v-shaped
104.5°
Electronegativity
The relative attraction that an atom in a molecule has for its shared pair of electrons in a covalent bond
What are some of the uses of electronegativity values?
- Predict which compounds are ionic and covalent
2. Predict the polarity of covalent molecules
If the difference in electronegativity values is greater than 1.7, then the compound is …
… ionic !
If the difference in electronegativity values is ~ 1.2 then the compound is …
.. highly polar covalent
If the difference in electronegativity values is ~ 0.9 then the compound is …
…. polar covalent
If the difference in electronegativity values is ~ 0.4 then the compound is …
… slightly polar covalent
If the difference in electronegativity values is ~ 0 then the compound is …
… non polar / pure covalent
Polar covalent bond
A bond in which there is unequal sharing of the pair (or pairs) of electrons. This causes one end of the bond to be slightly positive (δ⁺) and the other end to be slightly negative (δ⁻)
Why are there some molecules that have polar bonds but overall the molecule is non-polar?
This occurs when the central atom is positively charged and the negatively charges outside atoms cancel each other out due to symmetry
How might you show polarity experimentally?
- Allow liquid to flow from a burette
- Put a charged rod near the liquid
- If the liquid is moved by the rod it is polar (molecule has a charge)
- If the liquid is not deflected then it is non polar
What is the solubility rule?
like dissolves in like
Intramolecular bonding
Bonding that takes place within a molecule, i.e it holds the atoms together (ionic and covalent)
Intermolecular bonding
Forces of attraction that exist between molucules:
- Van der Waal
- Dipole-dipole
- Hydrogen bonding
Van der Waal forces
Weak attractive forces between molecules resulting from the formation of temporary dipoles. They are the only forces of attraction between non-polar molecules
How do Van der Waal forces form?
Temporary internal shift of electrons in a molecule lead to formation of temporary dipoles and small attractive forces
Dipole-dipole forces
Attractive forces between the negative pole of one polar molecule and the positive pole of another polar molecule
Hydrogen bonds
Particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine.
The hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in the other molecule.
Thus, the hydrogen bond acts as a bridge between two electronegative atoms in separate molecules
What is the range of boiling points for ionic compounds?
> 700°C
What is the range of boiling points for covalent compounds?
<700°C
What is the melting point of pure benzoic acid?
122.4°C
A pure substance melts…
sharply
An impure substance melts…
over a range of temps (e.g impure benzoic acid 114 - 118°C)
