Chapter 3“Atomic Structure”

Definition of an Atom

Dictionary definitionThe smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction; the number of protons determines the identity of the element.

Origin of word atom: Greek word “atomos” which means uncuttable, or indivisible, something that cannot be divided further.

Parts of the Atom

Parts of the Atom

Part Symbol ChargeMass

NumberMass in

amu

Proton p+ + 1 1 ~ 1 amu

Neutron no 0 1 ~ 1 amu

Electron e- - 1 0 ~ 0 amu

An electron weighs 1/1836 of a proton

What Does an Atom Look Like?- Let’s look at the Helium atom

Helium Atom

How small is an atom?

0.22 nanometers 0.00000000022 meters

What Makes Atoms Different From Each Other?

The number of PROTONS!!!

The atomic number (Z) equals the number of proton’sin an element’s atom.

Since elements on the periodic table are neutral (no charge),we can assume the # of electrons = # of protons.

The mass number equals the total number of protons andneutrons in the nucleus of an atom.

How Many Neutrons?

If we know the mass number then we can figure out how many neutrons are present by the following equation:

mass # - atomic # = # of neutrons

Q: How do we figure out what the mass number is???

A: Round the atomic mass on the periodic table to the nearest whole number

The mass number equals the total number of protons andneutrons in the nucleus of an atom.

NuclidesThe particles that make up the nucleus of an atom are called nuclides. The nuclide shows the mass number alongwith the atomic number (# of protons) of an atom.

# protons# neutrons# electrons

222

# protons# neutrons# electrons

# protons# neutrons# electrons

222622

3

34

What the Quark?Turns out protons and neutrons are made from smaller parts!! Uggh!

Quarks

Same Element Different Atom

All atoms of a particular element are not exactly alike. Some elements have atoms with different masses (isotopes)

Cool Down

What are two things you learned today? What do you still not understand?

Homework due Wednesday

Worksheets 4.1 and 4.2