1.3 Bonding Flashcards
What is a molecule?
A molecule is two or more atoms joined together by covalent bonds
(see below). A molecule is usually made up of non-metal atoms only.
Water (H2,O) is an example of a molecule. It has two hydrogen atoms and one oxygen atom all held together by bonds.
What is a covalent bond?
All elements in the periodic table want to be like a noble gas and have a full outer energy level. For example, neon has eight outer electrons where as oxygen only has six outer electrons so to become stable like a noble gas it must gain two electrons. Hydrogen has only one outer electron and will gain one more to achieve the same arrangement as helium.
To do this, the element has to form bonds. The bonds formed are called
covalent bonds.
Key points !
* A molecule is two or more atoms held together by covalent bonds.
* A covalent bond is a shared pair of electrons between two non-metal
atoms.
The atoms are held together because of the electrostatic force of
attraction between the positive nuclei of each atom and the negatively
charged electrons. This is better illustrated as a diagram.
The saying ‘opposites attract’ can be used to describe how a covalent
bond works. The positively charged nucleus is attracted to the
negatively charged electrons. However, the nucleus on the other side is
also attracted to them. This creates a ‘tug-of-war’ effect. Both nuclei
try to pull the electrons toward themselves creating a strong bond
that holds the atoms
Hydrogen has the electron arrangement of one. So by sharing electrons with
another hydrogen atom, they both have two outer electrons. This results in them having the same electron arrangement as the noble gas, helium.
What is a diatonic element?
Hydrogen is classed as a diatomic element because it exists not as a
single atom of hydrogen but as a pair of hydrogen atoms that share
electrons to become stable. There are other elements in the periodic
table that are also diatomic. In other words, they exist as pairs rather
than single atoms. For example, oxygen is a diatomic molecule; that is
why its formula is O2,. It is important to learn all seven diatomic elements.
Key points !
A diatomic element is made up of molecules that contain two atoms.
What are the diatomic elements?
Fluorine F2 Chlorine Cl2 Oxygen O2 Hydrogen H2 Nitrogen N2 Bromine Br2 Iodine I2
What are the shapes of molecules?
Tetrahedral (Such as CH4)
Pyramidal (Such as NH3)
Linear (Such as HF)
Bent (Such as H2O)
What is ionic bonding?
The saying opposites attract’ can be used to describe an ionic bond. The
attraction between oppositely charged particles is called an electrostatic
attraction.
Key points !
An ionic bond is an electrostatic force of attraction between a positive metal ion and a negative non-metal ion.
