Transcript Chapter 4 Atomic Structure

Atomic Structure
Part 2
History 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 Particles
 3 types of subatomic particles
• Protons: Positively charged particle (+) found in
the nucleus.
• Neutrons: Uncharged particle also found in the
nucleus.
• Electrons: Negatively charged particle (-) that
moves around the outside of the nucleus in the
electron cloud.
What makes atoms different
from one another?
 # of protons
 Atomic number = # of protons in the
atoms nucleus.
 The atomic number determines the
identity (what is it) of the atom.
How do you determine the
# of neutrons?
 Atomic mass = total number of #
protons and # neutrons in an atom’s
nucleus.
 Not all atoms of an element have the
same atomic mass number.
# of neutrons = atomic mass – atomic
number
What is the atomic mass of helium?
4.0026… round to 4
What element has an atomic mass of 27?
Aluminum
How many protons does this element
contain?
13
How many neutrons does this element
contain?
27 – 13 = 14
Isotopes
 Atoms of the same element that have
different numbers of neutrons in the
nucleus.
 The number of protons and electrons are
the same.
 Symbols:
23 or
Na
11
24
Na
11
12 or C13 or
C
6
6
14
C
6
Ions
 Formed when an atom gains or loses one
or more electrons.
 Occurs 2 ways:
• Positive Ion (+)
• Atom loses one or more electrons
• More protons than electrons, results in a (+)
charge
• Negative Ion (-)
• Atom gains one or more electron
• More electrons than protons, results in a (-)
charge
Examples of Ions




H+
ClAs3Mg2+
Lost 1eGained 1eGained 3eLost 2e-