Transcript Unit 2: Atom Notes

Review
• Scientist who discovered the electron using
the cathode ray tube
–Thomson
• Scientist who used the oil drop experiment to
discover the charge on the electron
–Millikan
• Scientist who conducted the gold foil
experiment to discover that the nucleus is
small, dense, and positively charged.
–Rutherford
Review
• Scientist that developed the pulsating
planetary model
–Bohr
• Scientist that discovered the existence of the
neutron
–Chadwick
• Scientist that had the solid sphere model of
the atom
–Dalton
Review
• Greek philosopher who coined the term atom
from the Greek word atomos
–Democritus
• Greek philosopher who did not believe in the
atom
–Aristotle
• Scientist who created the law of definite
proportions
–Proust
Review
• Scientist who created the law of multiple
proportions
–Dalton
• Scientist who created the law of conservation
of mass
–Lavoisier
Review
• An atom is the smallest particle of an
element that gives it its chemical and
physical properties.
• The atom is extremely small. One teaspoon
of water has 3 times as many atoms as the
Atlantic Ocean has teaspoons of water.
• If a large sports stadium were an atom, a
marble would represent the nucleus.
Atom Structure
An atom consists of a
• Positively charged nucleus that contains
protons and neutrons
• Negatively charged electrons in space outside
of the nucleus.
Electron cloud
Nucleus
Atoms found in nature have a neutral charge.
Why?
Atomic Number
All atoms of the same element
have the same number of
protons in the nucleus
13
Al
26.981
Atomic number
Atom symbol
AVERAGE Atomic Mass
Atomic Number
Atomic # = # protons =
# electrons
*only for neutral atoms
Mass Number
• Mass Number
= # protons + # neutrons
• NOT on the periodic table, electron
is so small that its mass is
negligible
Average Atomic Mass
• Weighted average, more
abundant isotopes have a
greater affect
–On the periodic table
Atomic Symbols
 Hyphen/mass notation - show the name of the
element, a hyphen, and the mass number in
sodium-23
 Nuclear symbol - show the mass number and atomic
number next to the chemical symbol
mass number
23 Na
atomic number
11
Figure 3.10: Two isotopes of
sodium.
Isotopes
• Atoms of the same element but
different mass number.
• Boron-10 (10B) has 5 p and 5 n
• Boron-11 (11B) has 5 p and 6 n
11B
10B
Practice
•Ar-40
•P-31
Isotopes?
Which of the following represent
isotopes of the same element?
Which element?
234
92
X
234
93
X
235
92
X
238
92
X
1. An __
___ is the smallest particle of
an element that has the chemical properties
of the element.
2. The 3 particles that make up the atom
are ________, _________, and _________.
3. Atoms with the same number of protons
and electrons, but a different number of
neutrons are called ____________.
4. ___________ was an English scientist
who developed an atomic theory in the
early 1800s.