What do atoms look like?

What do we know about atoms?

*All elements are composed of atoms*The atoms of the same element are the same (and different from the atoms of any other element)*Atoms of different elements can mix together or can chemically combine in a whole number ratio to form compounds* Chemical reactions occur when atoms are joined, separated or rearranged. BUT you can’t turn one element into another by chemical reaction.

What are atoms made of?

• The three basic components of an atom are the

–Proton

–Neutron

–Electron

Where are the subatomic particles found?

• Proton

• Neutron

• electron

• Found in the nucleus

• Has a +1 charge

• Mass of ~1amu

• 10-15 m in size

• p+

• Found in the nucleus

• Electrically neutral

• Mass of ~1amu

• 10-15 m in size

• n5

• Found outside the nucleus in the “electron cloud”

• Has a -1 charge

• Mass of ~0

• 10-18 m in size

• e-

MASS?

1 amu or “atomic mass unit” is 1/12 the mass of carbon 12

SIZE?

• The empty atom: If we imagine the atom’s nucleus to be the size of a bean, the atom itself will become the size of a stadium, and the electrons will be like tiny fleas whizzing frantically somewhere around the stands.

What makes the atoms of one element different from the atoms of

another?• The number of protons, neutron, and

electrons differs from one element to the next.

• The number of determines the element.

• The number of protons is equal to the on the periodic table

6

C12.011

Carbon

Atomic Number = # of Protons

• Every Hydrogen atom has ____ protons

• Every Magnesium atom has ____ protons

• Every Arsenic atom has ____ protons

Atoms are electrically neutral so…

# of protons must = # of electrons

How many electrons in an atom of Hydrogen?

Magnesium?

Arsenic?

The mass of an atom comes from its protons and neutrons so…

Mass Number = # of protons + # of neutrons

Or

Mass number – atomic number = # of neutrons

What is the difference between mass number and atomic mass?

• Atomic Mass= weighted average of the masses of all known isotopes of an element.

• Mass Number = protons + neutrons for a particular isotope of an element

***Round atomic mass to the nearest whole number to get the mass number for the most common isotope of that element.

How many neutrons in an atom of

Hydrogen?

Magnesium?

Arsenic?

Round the atomic mass to the nearest whole number

Why isn’t atomic mass a whole number?

Because elements exist as

Atoms with the same number of protons BUT a different number of neutrons

All atoms are isotopes, some are just more common then others!!!

Atomic mass is the weighted average of all the known isotopes of an element.

Isotopes are often represented using isotopic notation:

Mass number

Atomic number

Element symbol14

6

CEx.

• Many times the atomic number will be left off (since that always remains the same)

ex. Carbon-14

or14C

Did you know that carbon -14 is used to date fossils!

• Many times the atomic number will be left off (since that always remains the same)

ex. Carbon-14

or14C

What about IONS?

• Ions are electrically charged atoms

Positive = cation = more protons then electrons

Negative = anion = more electrons then protons

Represented as K+1