Download Atom

Democritus
• a Greek philosopher
(450 BC)
• Small indivisible units
of matter
• Called them “Atomos”
Atom
• Smallest particle of
an element that
retains the chemical
identity of that
element
Comparison
•World population:
7,000,000,000
•Atoms in Cu penny:
29,000,000,000,000,000,000,000
Molecule
• Smallest particle of
a compound that
retains the chemical
identity of the
compound
Law of Definite
Proportions (Proust)
•a compound always
contains the same
elements in the
same proportions
by mass
Percent by mass
% by mass =
100• element mass
compound mass
Problem:
•a 78.0 g sample of an
unknown compound
contains 12.4 g.
hydrogen. What is the
percent by mass of
hydrogen?
100 (12.4 / 78.0) = 15.9%
Problem #2
•If 3.5 g of X reacts with
10.5 g of Y to form XY,
what is the percent by
mass of X? … of Y?
25% X and 75% Y
Law of Multiple
Proportions (Dalton)
•Elements that
combine to form
multiple compounds
combine in specific
whole number ratios
for each compound.
Dalton’s Atomic Theory
• All matter is made up of extremely
small particles called atoms.
• All atoms of the same element are
exactly alike (mass, chemical
behavior,…) but they differ from
atoms of other elements.
• Atoms cannot be divided, created,
nor destroyed.
Dalton’s Atomic Theory -cont.
• Different atoms combine in
whole number ratios to form
compounds.
• Chemical reactions cause atoms
to separate, combine or
rearrange.
Electron
•Named for “elektron”,
an amber fossilized
tree sap
•First discovered
subatomic particles.
Thomson discovered the
negatively charged particles we
now call electrons.
Thomson’s Atom
•“plum pudding” model
pudding: + charge
raisins: - charge
Millikan’s Oil Drop Experiment
Rutherford’s Gold
Foil Experiment
Nucleus
•core or center of the
atom
Rutherford’s Atom
•small central positive
nucleus
•negative charges in
empty space around
nucleus.
Subatomic Particles
Symbol Location Charge
electron
proton
neutron
Mass
Subatomic Particles
Symbol Location Charge
electron
e−
proton
p+
neutron
n
Mass
Subatomic Particles
Symbol Location Charge
−
empty
space
electron
e
proton
p+
nucleus
neutron
n
nucleus
Mass
Subatomic Particles
Symbol Location Charge
−
empty
space
−1
electron
e
proton
p+
nucleus
+1
neutron
n
nucleus
0
Mass
Subatomic Particles
Symbol Location Charge
Mass
empty
space
−1
0.0005
amu
−
electron
e
proton
p+
nucleus
+1
1 amu
neutron
n
nucleus
0
1 amu
Atoms are
identified by
number of protons
Strong nuclear force
•holds the atom’s nucleus
together (protons +
neutrons)
•One of 4 basic
forces in nature
Review #1:
Who first came up with
the idea that matter is
made up of atoms?
Democritus
Review #2:
Dalton said matter is
made up of atoms which
cannot be?
divided, created,
destroyed
Review #3:
Is Dalton’s model a
law or a theory?
theory
Review #4
•What changes did
Thomson make to the
atomic model of Dalton’s
from about100 years
earlier?
#4
•Subatomic particles
(protons & electrons)
•Plum pudding model
Review #5
•What changes did
Rutherford make to
Thomson’s atomic
model?
#5
•Atoms are mainly empty
space
•Nucleus of protons &
neutrons
•Electrons in empty space
around nucleus
Subatomic Particles
• Protons
• Neutrons
• Electrons
Atomic number (Z)
• the number of protons
in an atom
• written just above the
chemical symbol on the
periodic table
Atoms are neutral
•Total # protons =
total # electrons
Mass number
• the number of protons
plus neutrons in an atom
14
N
7
or
N-14
“14” is mass #,
“7” is atomic #
15
N
7
N-16
Atomic mass unit
•unit of mass for atoms
•1 amu = 1/12th mass
of C-12 atom
•protons & neutrons are
appx. 1 amu
electrons are 0 amu
Ion: atom with an
electrical charge
Anion: more electrons
than protons: - charge
Cation: more protons
than electrons: + charge
25
2+
Mg
12
179
4+
Hf
72
37
−
Cl
17
Isotopes
–Atoms of the same
element that have
different numbers of
neutrons.
Iron-56
Fe-56
What has:
5 protons
6 neutrons
Atomic Mass
• average mass of an
element’s atoms
•averaged according to
their relative abundance
•sum of rel. abundances x
isotope mass
Atomic mass =?
93.12% K-39
6.88% K-41
(0.9312•39) + (0.0688•41)
= 39.14 amu
Find atomic #, mass #, #
p+, # n, & # e- for each:
۰ Ni-58
۰ Cl-36
۰ at.#40 & 51 n
۰ at.#47 & mass #107
۰ 30 p+ & 35 n
۰ mass #52 & 24 e-
Why is:
Atomic mass = 35.453
for Cl?
Shouldn’t it be a whole
number?