Atomic Structure

Elements

All elements are composed of only one type of atom. In these atoms are three subatomic particles:ProtonsNeutronsElectrons

Elements

-Protons have a positive charge (+)-Neutrons have no charge (neutral)-Electrons Have a negative charge (-)

• Most of the mass of an atom is found in the nucleus which contains the neutrons and protons.

Atomic number

• Atomic number tells you how many protons that elements has.

• If the number of protons changes, the element changes.

Atomic number

• Since the atom of an element is neutral, then the atomic number also tells you how many electrons you have.

Atomic # = # of protons = # of electrons

Atomic Mass

• Atomic mass is the total number of protons and neutrons found in the nucleus of an atom.

• # of protons + #of neutrons = atomic mass

Neutrons

• To find out how many neutrons and element has:

a) Round atomic mass to nearest whole numberb) Subtract atomic number from atomic mass to

get number of neutrons

Atomic Mass – Atomic Number = # of neutrons

Example

• Na (sodium)• Atomic mass is 22.989• Atomic mass rounded 23• Atomic number is 11Atomic Mass – Atomic Number = # of neutrons• 23-11= 12• Na has 12 neutrons.

Try these!!!

Co (Cobalt)

• Atomic mass is 58.933

• Atomic mass rounded 59

• Atomic number 27• 59-27= 32

Ag (Silver)

• Atomic mass is 107.868

• Atomic mass rounded 108

• Atomic number 47• 108-47 = 61.

Bohr’s model

• Is a physical drawing that shows where all the subatomic particles are located in a particular atom of an element.

• The Bohr’s model is similar to our very own solar system.

Bohr’s Model

• Protons and neutron are always found in the nucleus of the atom of an element.

• Electrons are around the atom in an area called the electron cloud.

• In this electron cloud are orbitals where electrons move around the nucleus of the atom.

Bohr’s Model

• Each orbital can only hold a certain amount of electrons:

• 1st orbital- 2 electrons• 2nd orbital- 8 electrons• 3rd orbital- 8 electrons• 4th orbital- 18 electrons

• The elements found in a group have similar properties because they have the same number of valence electrons.

• The horizontal rows on the periodic table are called a period. Periods tell you how many orbitals will be on your drawing.

• Ex. Na (sodium) is in Period 3, it will have 3 orbitals in its Bohr’s Model.

• The vertical columns on the periodic table are called groups. Groups tell you how many valence electrons the element has.

• Ex. Na (sodium) is in Group 1 so it has 1 valence electron.

• Valence electrons are the electrons that occupy the last orbital of an element.

• Orbitals are also called energy levels.

Boron (B)

5 p+

6 n

Al

13 p+

14 n

Lewis-Dot Structure

• The amount of dots you draw for a Lewis Structure (LS for short) is equal to the # of Valence Electrons in an Atom

Valence Electrons

• The # of Valence e- an atom has is dictated by the Group that the Element is in• Groups are the Vertical

Columns on the Periodic Table!!! It’s So Simple!!!!

• Isotopes are atoms of a given element that have different numbers of neutrons and different mass numbers.

• Ex. Oxygen-16; has 8 neutrons Oxygen-17; has 9 neutrons

Oxygen-18; has 10 neutrons

These are all still oxygen atoms.

• Elements on the periodic table are classified as one of the following:

• Metals• Nonmetals• Metalloids