S C I E N C E 9

MODELS OF THE ATOM

ALL ATOMS ARE NOT CREATED EQUAL

• Atoms can vary from one to the next of the same element in the number of neutrons they have in their structure• Two atoms that have the same number of protons

but different number of neutrons are called isotopes

• Carbon has three isotopes:• carbon-12• 6 protons, 6 neutrons, 6 electrons

• carbon-13• 6 protons, 7 neutrons, 6 electrons

• carbon-14• 6 protons, 8 neutrons, 6 electrons

HOW CAN THIS BE WRITTEN?

• There is a shorthand method for writing isotopes• It is called atomic notation• The mass number is written on the top left corner• The atomic number is written on the lower left

corner

CHARGED ATOMS ARE IONS

• Atoms are capable of gaining and losing electrons • When they lose or gain electrons, they are

called ions• The number of protons determines the identity of

an element • The number of electrons can change and the

element still remain the same• It is more common for atoms to have more or less

electrons than protons than for them to be equal to each other

EXAMPLE

• sodium atom (Na)• 11 protons, 12 neutrons, 11 electrons

• sodium ion (Na1+)• 11 protons, 12 neutrons, 10 electrons

• Protons are positively charged and electrons are negatively charged

• Ions have an unequal number of protons and electrons

ELECTRONS DETERMINE CHEMICAL COMBINATIONS

• Neils Bohr attempted to make a model of an atom to help explain the chemical behavior of atoms and ions

• Protons and neutrons are found in a nucleus• Outside the nucleus are electrons in pathways called

orbits• Electrons have energy and can move from one orbit to

another• The further an electron is from the nucleus, the more

energy it has• The number of electrons found in the first three orbits

is 2, 8, 8

BOHR MODEL OF THE ATOM

ENERGY AND ELECTRONS

• When an atom is energized, electrons move from a lower energy level to a higher one• The electrons move further away from the

nucleus• This is called an excited state

• When the electron releases its energy and moves back to the orbit with which is came, it is said to be in a ground state• The number of electrons that move from one orbit

to another coupled with the orbits within which they move give off specific colors of light

ATOMIC SPECTRA

• Every element on the periodic table, when given energy, produces a unique spectra of light• This is how

scientists identify unknown elements