Basic Chemistry

Atoms, Ions, Molecules and Polarity

Introduction

• Chemistry is the central science, meaning that all other science are based on chemistry.

• Why?– Because chemistry is the study of matter and

energy…specifically the atom

Building Blocks

• We will learn that in biology, the building block of life is the cell.

• In chemistry however, the building block of all matter is the atom.

Structure of the Atom

• For many years the atom was thought to be the smallest particle and that it could not be divided into anything smaller.

• Now we know that atoms are not the smallest particles. In fact, atoms are made of subatomic particles known as:– Protons– Neutrons– Electrons

General Structure

• There are two parts to the atom– Nucleus• A very small area in the center of the atom that

contains most of the mass.• The locations where protons and neutrons are found.

– Electron Cloud• The area of the electron that takes up the most space.• The location where the electrons are found.

Subatomic Particles

• Protons – The second largest particle in the atom– The number of protons determines the identity of

the atom– Located in the nucleus– Has a positive charge• Charge means that an object has an attraction to some

objects and is repelled by another.• In this case the proton is attracted to negatively

charged particles.

Subatomic Particles

• Neutrons– The largest particle in the atom– The number of neutrons in an atom greatly

impacts the mass of the atom. – Located in the nucleus– Has a neutral charge• Charge means that an object has an attraction to some

objects and is repelled by another.• In this case the neutron has no charge and therefore

does not attract any other particles.

Subatomic Particles

• Electrons– The smallest of the three major particles – The interaction of electrons give the atom it’s

characteristics– Located in the electron cloud– Has a negativecharge• Charge means that an object has an attraction to some

objects and is repelled by another.• In this case the electron has a negative charge and

attracts positively charged particles.

Neutral Atoms

• Atoms typically have the same number of protons and electrons making them neutral.

• Just as with the neutrons, when a substance is neutral there is not attraction to another particle.

• If atoms always stayed neutral, there would be no interaction between atoms and the world would be left with about 92 different objects only instead of the trillion or more that exist today.

Ions

• The electrons determine the characteristics of the atom.

• Thus the interaction between atoms to form compounds is a result of the interaction between electrons.

• In the process of interacting atoms sometimes gain or lose electrons in the process forming ions.

Formation of Ions: Losing Electrons

• Losing electrons– A large group of elements wants to lose electrons.

This group is called the metals.– When a element loses electrons the overall charge

on the atom becomes positive.• This is because the atom now has more positives than

negatives.• Protons can NEVER be gained or lost so gaining and

losing electrons is the only way to change the charge on the normally neutral atom.

Formations of Ions

• Gaining electrons– A smaller group of elements wants to gain

electrons. This group is called the non-metals.

Formation of Ions: Gaining Electrons

• Losing electrons– A smaller group of elements wants to lose

electrons. This group is called the non-metals.– When a element gains electrons the overall charge

on the atom becomes negative.• This is because the atom now has more negativesthan

positives.• Protons can NEVER be gained or lost so gaining and

losing electrons is the only way to change the charge on the normally neutral atom.

Ion Formation and Bonding

• The ability of an atom to gain or lose electrons allows that atom to interact, or bond, with another atom to form a completely new substance.

Bonding

• There are two types of bonding that can occur – Ionic bonding• Caused by the transfer of electrons from one atom to

another

– Covalent bonding• Caused by the sharing of electrons between different

atoms.

Ionic Bonding

• In ionic bonds, ions are formed creating two oppositely charged particles.– One or more atoms transfers their electron to another

atom.• The atom that does the transferring loses electrons and

becomes positive.• The atom that does the receiving gains electrons and becomes

negative.

– The attraction between the two charged particles results in a compound being formed.• This compound has very different properties than the

elements involved in the formation.

Covalent Bonding

• In covalent bonding, nonmetal elements share their electrons.– When electrons are shared between atoms they

interact forming a new compound. – This compound usually has very different

properties than the elements that are bonded together.

Unequal Sharing

• When atoms share electrons, there are two different ways in which they can be shared– Equally• These form non-polar molecules

– Unequally• These form polar molecules

Non-Polar Bonds

• Polarity is determined by the location of the electrons between two atoms.

• When atoms share the electrons equally, the electrons spend as much time with one atom as they do another essentially seeming as if they are in the middle.

Polar Bonds

• When atoms share the electrons unequally, the electrons spend more time with near the nucleus of one atom than the other, essentially seeming as if it were at one pole or another.

• Imagine the poles of the earth. They are located at one extreme or the other. This is how the electrons in this type of bond can be pictured.