Atomic StructureAtomic StructurePart 2Part 2

History of the AtomHistory of the Atom

Democritus (Greek 460-370 BC)• 1st to use the word atom• Believed that atoms were indivisible & indestructible• No scientific support

Aristotle (Greek 384-322 BC)• Rejected the theory of atoms• Believed in 4 core elements

fire, air, water, earth

Subatomic ParticlesSubatomic Particles

33 types of subatomic particles types of subatomic particles• Protons: Protons: Positively charged particle (+) found in Positively charged particle (+) found in

the nucleus.the nucleus.

• Neutrons: Neutrons: Uncharged particle also found in the Uncharged particle also found in the nucleus.nucleus.

• Electrons: Electrons: Negatively charged particle (-) that Negatively charged particle (-) that moves around the outside of the nucleus in the moves around the outside of the nucleus in the electron cloud.electron cloud.

What makes atoms different What makes atoms different from one another?from one another?

# of protons# of protons Atomic numberAtomic number = # of protons in the = # of protons in the

atoms nucleus. atoms nucleus.

The atomic number determines the The atomic number determines the identity (what is it) of the atom.identity (what is it) of the atom.

How do you determine How do you determine the # of neutrons?the # of neutrons?

Atomic massAtomic mass = total number of # = total number of # protons and # neutrons in an atom’s protons and # neutrons in an atom’s nucleus. nucleus.

Not all atoms of an element have the Not all atoms of an element have the same atomic mass number.same atomic mass number.

# of neutrons = atomic mass – atomic # of neutrons = atomic mass – atomic numbernumber

What is the atomic mass of helium?What is the atomic mass of helium?

What element has an atomic mass of 27?What element has an atomic mass of 27?

How many protons does this element How many protons does this element contain?contain?

How many neutrons does this element How many neutrons does this element contain?contain?

4.0026… round to 4

Aluminum

13

27 – 13 = 14

IsotopesIsotopes Atoms of the Atoms of the samesame element that have element that have

differentdifferent numbers of neutrons in the numbers of neutrons in the nucleus.nucleus.

The number of protons and electrons are The number of protons and electrons are the same.the same.

Symbols:Symbols:

1111NaNa2323 or or 1111NaNa2424

66CC1212 or or 66CC1313 or or 66CC1414

IonsIons Formed when an atom gains or loses one Formed when an atom gains or loses one

or more electrons.or more electrons. Occurs 2 ways:Occurs 2 ways:

• Positive Ion (+)Positive Ion (+)• Atom loses one or more electronsAtom loses one or more electrons

• More protons than electrons, results in a (More protons than electrons, results in a (++) ) chargecharge

• Negative Ion (-)Negative Ion (-)• Atom gains one or more electronAtom gains one or more electron• More electrons than protons, results in a (More electrons than protons, results in a (--) )

chargecharge

Examples of IonsExamples of Ions

HH++

ClCl--

AsAs3-3-

MgMg2+2+

Lost 1eLost 1e--

Gained 1eGained 1e--

Gained 3eGained 3e--

Lost 2eLost 2e--