Chemical Bonding Flashcards
Water formula
H2O
Two hydrogen atoms joined to one oxygen atom
Methane formula
CH4
An atom of carbon joined to four atoms of hydrogen
Which chemical bonds do you have to describe in examinations
H2
O2
H20
CH4
Why are noble gases so unreactive
Elements that have eight electrons in their outer orbit are very unreactive.
The eight electrons in the outer orbit are a stable octet
Octet rule
When bonding occurs, atoms try to have eight electrons in the outer orbit
Octet rule exceptions
Helium does not have eight electrons in its outer orbit but it’s first and only orbit of electrons is full and is always classifies with the inert gases as its properties are so similar
Hydrogen and lithium tend to teach the electron configuration of helium when chemical bonding occurs
Covalent bond
A covalent bond is a bond that consists of shared electrons.
Atoms try to get eight electrons in their outer orbit by sharing electrons with other atoms
Hydrogen molecule bond
H2.
The orbits of two hydrogen atoms overlap and share their atom with the other. This gives each atom the stable electron configuration of helium (two electrons in the outer orbit). Each atom has its own electron and a shared electron. The sharing of a pair of electrons is known as a single covalent bond. H - H
Methane molecule bond
CH4.
A molecule of methane is one atom of carbon joined to four atoms of hydrogen.
C = 2, 4
H = 1
Carbon needs four more electrons in its outer orbit to get noble gas configuration. It shares each of its four outer electrons with a hydrogen atom.
Molecule
A molecule is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently
Water molecule bond
H2O
One atom of oxygen joined to two atoms of hydrogen.
O = 2, 6
H = 1
Oxygen has 6 electrons in its outer orbit so it needs 2 more to get noble gas configuration.
It shares two of its six atoms with two hydrogen atoms
Oxygen molecule bond
02
Two oxygen atoms joined together
O = 2, 6
Oxygen has six electrons in its outer orbit and needs two more to get noble gas configuration.
Single bond
A single bond is formed when one pair of electrons is shared.
Double bond
Represented by ( ) = ( ) double dash A double bond is formed when two pairs of electrons are shared.
Ionic bond
An ionic bond is the force of attraction between positive and negative ions in a compound
Ions
An ion is a charged ion or group of ions.
Table salt consists of particles called ions and are represented as Na+ and Cl-
Na+ = sodium ion. Lost an electron which are negatively charged so it is positively charged
Cl- = chloride atom. Gained an electron which are positively charged so it is negatively charged.
Sodium chloride ionic bond
NaCl
Na = 2, 8, 1 (loses one electron) Na+ = 2, 8
Cl = 2, 8, 7 (gains an electron) Cl- = 2, 8, 8
Sodium loses its one atom in the outer orbit so it has a full outer shell and gives it to chlorine so it has a full outer shell.
Magnesium oxide ionic bond
MgO
Mg = 2, 8, 2 (loses two electrons) Mg2+ = 2, 8
O = 2, 6 (gains two electrons) O2- = 2, 8
Magnesium gives its two atoms in its outer orbit to oxygen so oxygen has a full outer shell.
Magnesium ion
Oxide ion
Properties of ionic compounds
- Ionic compounds are usually solid at room temperature because of the attraction between the oppositely charged ions. In sodium chloride, the attraction is so strong that it forms a definite shape and crystals.
- They have a high melting and boiling point because it takes a lot of energy to separate the strongly attracted ions, NaCl melting point = 800c. NaCl boiling point = 1500c.
- They dissolve in water because water is attracted to ions and they are pulled away into solution
- They conduct electricity when melted or dissolved because the ions are free to move.
Properties of covalent compounds
- Usually a liquid or gas at room temperature because the atoms in the molecules are held together by covalent bonds but no strong forces of attraction between the molecules, e.g. water and methane.
- Low melting and boiling points as not much energy is needed to separate the molecules as there are no strong forces of attraction between the molecules.
- Many don’t dissolve in water because they don’t contain ions which water is attracted to.
- They do not conduct electricity because they do not contain ions
To investigate the ability of ionic me covalent substances to conduct electricity
Apparatus : power supply, bulb, leads, crocodile clips, carbon electrodes, wash bottles
Chemicals : water, copper sulfate solution, methylated spirits, sodium chloride solution, table sugar solution, paraffin oil
Method :
1. Set up the apparatus as shown in the diagram
2. Insert the carbon electrodes in the copper sulfate solution.
3. Write down what you observe.
4. Repeat with other solutions, washing the carbon electrodes with the wash bottles between solutions
Conclusion : solutions that contain ions conduct an electric current
