Download Defining the Atom

2.2
Defining the Atom
> Early Models of the Atom
II. The Atom: smallest particle of an element that
retains its identity in a chemical reaction.
a. Proposed first by Democritus
who said atoms were indivisible
and indestructible (400 BC)
b. Dalton (1800): atoms of any one
element are different from those of any other; atoms
of the same element are identical; and different
atoms can form mixtures or can chemically combine
in simple whole-number ratios to form compounds.
Slide
1 of 18
© Copyright Pearson Prentice Hall
2.2
Defining the Atom
> Sizing up the Atom
Iron Atoms Seen Through a Scanning
Tunneling Microscope
Slide
2 of 18
© Copyright Pearson Prentice Hall
2.2
Defining the Atom Subatomic
Particles
>
A. Subatomic Particles: there are three
1. Protons: positively charged, in the nucleus
a. Discovered1886, by Eugen Goldstein
b. Large mass
2. Neutrons: no charge, in the nucleus
a. Discovered 1932, by James Chadwick
b. Mass nearly equal to that of a proton.
3. Electrons: are negatively charged
a. J. J. Thomson discovered in 1897
b. Mass of proton / 1840
© Copyright Pearson Prentice Hall
Slide
3 of 18
4.2
Defining the Atom
> Subatomic Particles
5. Summarizes the properties (copy table)
Slide
4 of 18
© Copyright Pearson Prentice Hall
4.2
Defining the Atom
> The Atomic Nucleus
6. Shape of the Atom:
a. Thompson said the atom was filled with
positively charged material and the electrons
were particles evenly distributed.
b. Ernest Rutherford (1871–1937) directed a
narrow beam of alpha particles at a very thin
sheet of gold foil & found almost all of the
mass concentrated in a small volume, the
nucleus.
i. atoms mostly low density space (electrons)
c. nucleus: tiny central core, composed of
protons and neutrons.
© Copyright Pearson Prentice Hall
Slide
5 of 18
4.2
Defining the Atom
> The Atomic Nucleus
d. electrons are distributed around the nucleus and
occupy almost all the volume of the atom.
Slide
6 of 18
© Copyright Pearson Prentice Hall
2.2
Defining the Atom Atomic
Number
>
B. Distinguishing Among Atoms
a. Different elements contain different
numbers of protons.
1. Atomic Number: number of protons in the
nucleus & the number of electron in a neutral
atom.
a. Periodic table arrange by this number.
2. Mass Number: total number of protons and
neutrons.
a.
Slide
7 of 18
© Copyright Pearson Prentice Hall
4.3
Defining the Atom
> Atomic Number
Slide
8 of 18
© Copyright Pearson Prentice Hall
2.2
Defining the Atom
>
Isotopes
3. Isotopes: atoms that have the same number of
protons but different numbers of neutrons and mass
numbers.
a. Chemically alike because of identical
numbers of protons and electrons.
Slide
9 of 18
© Copyright Pearson Prentice Hall
4.3
Defining the Atom
> Atomic Mass
4. Atomic Mass: weighted average mass of the
atoms in a naturally occurring sample of the
element.
a. Reflects both the mass and the relative
abundance of the isotopes.
b. atomic mass unit (amu) is defined as one
twelfth of the mass of a carbon-12 atom.
c. Example: Calculating atomic mass
Slide
10 of 18
© Copyright Pearson Prentice Hall
4.3
Defining the Atom
> Atomic Mass
Weighted Average Mass of a Chlorine Atom
3 of 4 Cl atoms are Cl-35
1 of 4 Cl atoms are Cl-37
Slide
11 of 18
© Copyright Pearson Prentice Hall
Defining the Atom
Physical Science: PROFICIENCY PRACTICE
> 119
P.12.A.2 http://www.rpdp.net/sciencetips_v2/P12A2.htm
119. The figure to the right shows part of the
periodic table.
Which of the following is an accurate
comparison of the atomic number and mass of
copper (Cu) and gold (Au)?
A. Au has a smaller atomic mass and fewer
electrons than Cu.
B. Au has the same atomic mass as Cu but a
greater atomic number.
C. Au has the same atomic number as Cu but
a much greater atomic mass.
/
D.
Au has both a greater atomic number and
a greater atomic mass than Cu.
© Copyright Pearson Prentice Hall
29
Copper
Cu
63.55
47
Silver
Ag
107.9
79
Gold
Au
197.0
Slide
12 of 18
Defining the Atom
Physical Science : PROFICIENCY PRACTICE
> 123
P.12.A.8 http://www.rpdp.net/sciencetips_v2/P12A8.htm
123. The mass number of an element is
the total number of protons and
neutrons located in the nucleus. If
carbon has an atomic number of 6 and a
mass number of 12, how many neutrons
does it contain?
A. 0
B. 6
C. 12
D. 18
Slide
13 of 18
© Copyright Pearson Prentice Hall
Defining the Atom
> 4.1
Slide
14 of 18
© Copyright Pearson Prentice Hall
4.1 Section Quiz
1. The ancient Greek philosopher credited with
suggesting all matter is made of indivisible
atoms is
a. Plato.
b. Aristotle.
c. Democritus.
d. Socrates.
Slide
15 of 18
© Copyright Pearson Prentice Hall
4.2 Section Quiz
5. The nucleus of an atom consists of
a. electrons only.
b. protons only.
c. protons and neutrons.
d. electrons and neutrons.
Slide
16 of 18
© Copyright Pearson Prentice Hall
4.2 Section Quiz
6. Most of the volume of the atom is occupied
by the
a. electrons.
b. neutrons.
c. protons and neutrons.
d. protons.
Slide
17 of 18
© Copyright Pearson Prentice Hall
4.3 Section Quiz
7. Isotopes of an element have
a. the same mass number.
b. different atomic numbers.
c. the same number of protons but different
numbers of neutrons.
d. the same number of protons but different
numbers of electrons.
Slide
18 of 18
© Copyright Pearson Prentice Hall
4.3 Section Quiz
8. How many neutrons are in sulfur-33?
a. 16 neutrons
b. 33 neutrons
c. 17 neutrons
d. 32.06 neutrons
Slide
19 of 18
© Copyright Pearson Prentice Hall