Elements:

  • Are pure substances with only one type of atom.
  • Each element has its own distinct properties.
  • Elements cannot be broken down into simpler parts by a chemical change.

Compounds:

Are pure substances made of more than one type of atom.

Compounds are made of elements.

For example:

Na (sodium) and Cl (chlorine) are examples of elements.

You can have one sodium atom and one chlorine atom.

Add one Na and one Cl together:

NaCl (sodium chloride) is an example of a compound.

It contains 1 atom of sodium and 1 atom of chlorine.

Elements in the Periodic Table

All elements have been given symbols like Na and Cl.

All sodium atoms look and behave the same way.

They have the same chemical and physical properties.

All elements are organized according to chemical property in the periodic table.

For example:

Elements in the periodic table are classified as being metals, non-metals and metalloids.

Metals have good malleability and ductility. Non-metals include gases and do not conduct electricity.

The Language of Chemistry

Chemical formula:uses symbols and numbers to represent what types of atoms are in a compound.

Molecule:a group of atoms bonded together. (Yes, compounds are molecules!)

Word Equations:describe chemical changes or chemical reactions.

sodium + chlorine  sodium chloride

Na + Cl  NaCl

What Are Atoms Made Of?

Atoms consist of:

1.A nucleus made of positively charged protons and non-charged neutrons.

2.A group of organized negatively charged electrons.

Electrons are organized into compartments or orbitals called “shells”.

Each element has a different number of electrons, protons and neutrons.

The atomic number is the number of electrons.

Helium has 2 electrons.

Neutral Atom and Ions

Neutral Atoms and Ions

Neutral atoms have equal numbers of positively charged protons and negatively charged electrons.

Ions have unequal numbers of protons and electrons.

For example:

Na (sodium) has 11 electrons and 11 protons when it is neutral.

If sodium has 12 electrons we say it is a negatively charged ion.

This is because it has one extra electron. (12 electrons, but still 11 protons)

If sodium has 10 electrons, it is called a positively charged ion because it has one fewer electrons. (10 electrons, but still 11 protons).

Remember: protons have a positive charge (+)

Electrons have a negative charge (-)

Bohr-Rutherford Diagrams

Electrons are arranged around the nucleus in groups or orbitals containing 2 and then 8 electrons in the second and third. The fourth has 18.

Neon has 10 electrons.

Valence Electrons

These are the electrons in the last orbital or shell.

Remember, electrons are organized around the nucleus in orbits containing 2, 8,8 or18…electrons.

THE COMBINING CAPACITY OF ELEMENTS

In order for elements to combine chemically with one another (i.e. bond), an interaction (e.g. "sharing" or "taking") of the outermost (valence) electrons is necessary.

The number of valence electrons can be determined from your Bohr-Rutherford diagrams or by using the group number of the element in question.

For example:

When elements combine to form other substances, they then become molecules.

Each atom in a molecule wants to pair up all of its electrons.

This means that those mainly on the right of the period table will want to have 8 electrons surrounding them, while those on the left side of the periodic table will "donate" their electrons to the bond. You’ll see this usually means sharing 8 electrons. Therefore, we call this the "octet rule".