Journal #201. Who discovered the electron?2. What did Rutherford discover?

Atomic Structure

Learning Goal:Today, we will identify the number of protons,

neutrons and electrons for a given element.

AtomsElements consist of atoms.An atom is the smallest unit of an element

that has the chemical properties of that element.

Atomic Structure Even though elements are very tiny, they are

made up of smaller parts called subatomic particles.

There are 3 kinds of subatomic particles:Protons- positive chargeNeutrons-no chargeElectrons-negative charge

The NucleusThe nucleus is the small region in the center

of an atom.The nucleus has a positive charge because it

contains only protons and neutrons.

The Electron CloudElectrons move around the nucleus in a space

called the electron cloud.

Atomic NumberThe atomic number is equal to the number of

protons in an atom.Example:

Carbon has an atomic number of 6. That means it has 6 protons

Elements on the periodic table are ordered according to their atomic number.

Number of electronsFor all neutrally charged elements, the

number of protons equals the number of electrons:

Example:Oxygen has an atomic number of 8.

8 protons8 electrons

Atomic MassThe atomic mass is equal to # of protons + #

neutrons.Example:

Carbon has an atomic mass of 12 and an atomic number of 6. Therefore :

12(mass)-6(protons)= 6 neutrons

IsotopesAlthough all atoms of a given element contain

the same number of protons, the number of neutrons may differ.

Isotopes are named according to their atomic mass

Example:Most helium atoms have 2 neutrons, some

helium atoms only have one neutron.

Let’s Practice:1. For the element Oxygen: identify the

number of protons, neutrons and electrons.2. For the element Carbon-13: identify the

number of protons, neutrons and electrons3. For the element Hydrogen- identify the

number of protons, neutrons and electrons