Download Atoms, Elements, and Ions

Atoms, Elements,
and Ions
The Language of Chemistry
• CHEMICAL ELEMENTS
-
– pure substances that cannot be decomposed by
ordinary means to other substances.
Aluminum
Sodium
Bromine
Lesson 1
The Atom: From Idea to Theory
Essential Question
• How has the theory of the atom
evolved over time?
Objectives
• To summarize Dalton’s atomic
theory.
• To explain the laws that support
Dalton’s atomic theory.
The Atom
An atom consists of a
• nucleus
–(of protons and neutrons)
• electrons in space about the nucleus.
Electron cloud
Nucleus
The Structure of An Atom
• An atom is the smallest particle of
an element that has the chemical
properties of the element.
Copper
atoms on
silica
surface.
Distance across = 1.8 nanometer (1.8 x 10-9 m)
History of the atom
• Not the history of atom, but the idea
of the atom.
• Original idea began
1. Ancient Greece (400 B.C.)
»Democritus- Greek philosopher
• “father of modern science”
2. India (600B.C.)
1.Hindu Nyaya philosophy
Not really sure which one.
History of Atom
• Looked at beach
• Made of sand
• Cut sand - smaller
sand
Smallest
possible
piece?
Atomos - not to be
cut
Another Greek
• Aristotle - Famous natural philosopher
• Believer of the 4 earthly elements
– Fire - Hot
– Air - light
– Earth - cool, heavy
– Water – wet
• Plus one of his own
»Aether – divine/heavenly bodies
• Blend these elements in different
proportions to get all substances
Who Was Right?
•
•
•
•
Greek society was slave based.
Beneath famous to work with hands.
Did not experiment.
Greeks settled disagreements by
argument.
• Aristotle was more famous, so he won.
• His ideas carried through middle ages.
• Later, Alchemists attempted to change
lead to gold.
Who’s Next?
• Late 1700’s - John Dalton- from England.
–Math & natural philosophy tutorsummarized results of his experiments and
those of others.
• Dalton’s Atomic Theory
• Combined ideas of elements with that of
atoms.
Dalton’s Atomic Theory
1. matter is composed, indivisible particles
(atoms)
2. all atoms of a particular element are identical
3. different elements have different atoms
4. atoms combine in certain whole-number
ratios
5. Chemical reactions involve the
rearrangement of atoms.
 No atoms are created, destroyed, or
changed into atoms of any other elements.
Dalton’s support for his theory
• Law of Conservation of Mass – Mass
is neither created nor destroyed
during ordinary chemical reactions.
• Let’s look at an equation:
• 2H2 + O2 >> 2H2O
• The quantity and mass of reactants
equals the quantity and mass of the
products.
Problems with Dalton’s Atomic Theory?
1. matter is composed, indivisible particles
Atoms Can Be Divided, but only in a nuclear
reaction
2. all atoms of a particular element are identical
Does not Account for Isotopes (atoms of the same
element but a different mass due to a different
number of neutrons)!
3. different elements have different atoms
YES!
4. atoms combine in certain whole-number ratios
YES! Called the Law of Definite Proportions
5. In a chemical reaction, atoms are merely rearranged
to form new compounds; they are not created,
destroyed, or changed into atoms of any other
elements.
Yes, except for nuclear reactions that can change
atoms of one element to a different element
Modern Atomic Theory
• We know today that atoms are made
of electrons, protons, neutrons.
• We will study that next.
Even More Modern Atomic
Theory
• Known as the Standard Model
• protons & neutrons are made of
six different “flavors” of quarks.
• Electrons are made of leptons
Plus there’s more
• Fermions
Baryons
• Neutrinos
Gluons
• Higgs-Boson – the most fundamental
particle
• Not to mention that EVERY particle of
matter has an antimatter counterpart.
• But we are not studying this stuff!
Learning Check 1a
1. C + O2 >> ?? According to the
Law of Conservation of Mass, the
correct answer for the product
is:
A.
B.
C.
D.
CO
C2O
CO2
C1/2O
Learning Check 1b
• Which of Dalton’s statement(s) is NO longer
correct today?
1. All matter is composed of atoms.
2. Atoms of any given element are identical, and
are different than atoms of another element.
3. Atoms cannot be created, destroyed, or
subdivided.
4. Atoms of different elements combine in whole
number ratios.
5. In chemical reactions, atoms are combined,
separated, or rearranged.
Isotopes-atoms of an element with different # neutrons
Nuclear fission – splitting an atom
Learning Check 1c
• Explain how an idea, an opinion, a theory,
and a law all become connected?
• First, someone has an idea; then persuades
others to believe, which is an opinion.
Skeptical people need proof. Experiments and
data provide proof which creates a theory.
After many, many years of experiments trying
to disprove without success, a theory
becomes a law.
Lesson 2
Structure of the Atom
Essential Question
• How has scientific discovery and technology
supported the structure of the atom?
Objectives
• To summarize the experiments that contributed to
the structure of the atom.
–Describe the structure of an atom including
location of protons, electrons, and neutrons with
respect to the nucleus.
–Distinguish among protons, electrons, and
neutrons in terms of relative mass and charge.
Parts of Atoms
• J. J. Thomson - English physicist.
(1897)
• Made a piece of equipment called a
cathode ray tube.
• It is a vacuum tube - all the air has
been pumped out.
Thomson’s Experiment
Voltage source
-
+
Vacuum tube
Metal Disks
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
• By adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field he found
that the moving pieces had a negative
charge
More from Thomson
• JJ Thomson third experiment confirmed that the
negative charge was coming from very tiny
particles (1000x smaller than hydrogen atom) and
were not rays. He called them electrons.
• In 1904 Thomson proposed his model of an
atom.
– Original knickname - Plum Pudding Model
– Today’s knickname – Blueberry Muffin model (Why?)
Millikan’s Experiment (1909)
• Millikan determined the size of the charge of
an electron.
• He put a charge on a tiny drop of oil and
measured how strong an electric field had to
be in order to stop the oil drop from falling.
Rutherford’s experiment
• Ernest Rutherford -English physicist.
(1911)
– Believed in Thomson’s model of the atom (1904).
– Wanted to see how big they are.
– Used radioactivity.
– Alpha particles - positively charged pieceshelium atoms minus electrons
– Shot them at gold foil which can be made a few
atoms thick.
Rutherford’s experiment
• When an alpha particle hits a fluorescent
screen, it glows.
• Here’s what it looked like
Lead
block
Uranium
Fluorescent
Screen
Gold Foil
He Expected
• The alpha particles to pass through
without changing direction very much.
• Because…?
• …the positive charges were thought to
be spread out evenly. Alone they were
not enough to stop the alpha particles.
What he expected
Because
He thought the mass was evenly
distributed in the atom
Since he thought the
mass was evenly
distributed in the atom
What he got
How he explained it
• Atom is mostly empty.
• Small dense,
positive piece at center.
• Alpha particles
are deflected by it if they get close
enough.
+
+
Density & the Atom
Conclusion
• Since most of the particles went through, it
was mostly empty space.
• Because the pieces turned so much, the
positive pieces were heavy.
• Small volume, big mass, big density.
• This small dense positive area is the
nucleus.
Learning Check 2a
Subatomic particles
Relative
Name Symbol Charge mass
Actual
mass (g)
Electron
e-
-1
0.0055 9.11 x 10-28
Proton
p+
+1
1
1.67 x 10-24
Neutron
n0
0
1
1.67 x 10-24
Learning Check 2b
B
C
Scientist
Discovery
Rutherford
A. Mass of electrons
Thomson
B. Positive charge of
nucleus
C. negative charge of
electrons
Millikan
A
More on Rutherford
• 1911 – he named the center of atom
nucleus, meaning “little nut.”
• Designed a model of the atom
• 1920 – After further experiments
Rutherford named the + charged
particles in the nucleus – protons.
• He predicted that there was a mass
of neutral charge particles in the
nucleus, but did not conduct any
experiments.
Rutherford Atom Model
no neutrons yet
Discovery of the neutron
• It was known, but not understood, that
the A was approximately twice the value
of the Z for an element.
• 1932 James Chadwick conducted
experiments using radioactive material.
• Discovered a particle in the nucleus with
no charge – called it the neutron.
Atomic Theory- Law of Definite
Proportions
• Law of Definite Proportions:
–A chemical compound has the same
exact proportions by mass regardless
of the size of the sample or source of
the compound.
–Ex: The composition of pure water H2O
is ALWAYS be 11.2% hydrogen and
88.8% for oxygen by mass.
Example 1
Law of Definite Proportions
Worksheet
1.Remember your Rules of
Significant Figures
1. Multiply/Divide – Limiter is the value
with least amount of sig figs.
2. Add/Subtract – Limiter is value with
least amount of decimals.
2. When multiplying by 100%, the %
sign is the unit of measure. Do not
unit % key on calculator.
Example 2
• A sample of sodium chloride NaCl
weighing 175.35g contains 60.6% Cl by
mass.
1. How many grams of Cl are in the
sample?
2. How many grams of Na are in the
sample?
Percent Composition Worksheet
You will need a Calculator and a Periodic
Table.
1.For every compound determine how many
atoms of each element are present.
2.Find the mass of each element in the
compound on the P.T. (Round 2 decimal
places)
3.Calculate the sum of the masses of the
elements, call this the total mass.
4.Divide the mass of the element by the total
mass, then multiply by 100%.
% Composition: Example
Laws Pertaining to Atomic TheoryLaw of Multiple Proportions
• Law of Multiple Proportions
– Is when 2 elements combine to form more than one
compound. The ratio of the masses of the second element
when combined with a certain mass of the first element is
ALWAYS a ratio of the small whole numbers.
– Ex:CO vs. CO2. In CO 1.33g oxygen combine with 1g carbon,
while in CO2,there are 2.66g of oxygen that combine with 1g
carbon.
Lesson 3
Counting Atoms
Essential Question
How do you distinguish between an atom, an ion,
and an isotope?
Objectives
• To calculate the atomic number, mass
number, and average atomic mass.
• To explain what isotopes are.
ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
Remember:
HOFBrINCl
Hockey Stick and the Puck
These elements
only exist as
PAIRS. Note that
when they
combine to make
compounds, they
are no longer
elements so they
are no longer in
pairs!
ATOM
COMPOSITION
The atom is mostly
empty space
•protons and neutrons in
the nucleus.
•the number of electrons is equal to the
number of protons.
•electrons in space around the nucleus.
•extremely small. One teaspoon of water has
3 times as many atoms as the Atlantic Ocean
has teaspoons of water.
ATOMIC COMPOSITION
• Protons (p+)
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic
mass units (amu) but we can round to 1
• Electrons (e-)
–
negative electrical charge
– relative mass = 0.0005 amu
but we can round to 0
• Neutrons (no)
no electrical charge
– mass = 1.009 amu but we can round to 1
–
Atomic Number, Z
All atoms of the same element
have the same number of
protons in the nucleus, Z
27
Al
13
Mass Number
Symbol
Atomic number
Mass Number, A
• C atom with 6 protons and 6 neutrons
is the mass standard
• = 12 atomic mass units
• Mass Number (A)
= # protons + # neutrons
• This is NOT on the periodic table…(that
is the AVERAGE atomic mass)
• A boron atom has
A = 5 p + 5 n = 10 amu
A
10
Z
5
B
Isotopes
• Atoms of the same element (same Z)
but different mass number (A).
• Boron-10 (10B) has 5 p and 5 n
• Boron-11 (11B) has 5 p and 6 n
11B
10B
Figure 3.10: Two isotopes of
sodium.
Isotopes &
Their Uses
Bone scans with
radioactive
technetium-99.
Isotopes & Their Uses
The tritium content of ground water is
used to discover the source of the water,
for example, in municipal water or the
source of the steam from a volcano.
Atomic Symbols
 Show the name of the element, a hyphen, and
the mass number in hyphen notation
sodium-23
 Show the mass number and atomic number
in nuclear symbol form
mass number
23 Na
atomic number
11
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
Counting Protons, Neutrons,
and Electrons
• Protons: Atomic Number (from periodic table)
• Neutrons: Mass Number minus the number of protons
(mass number is protons and neutrons because the
mass of electrons is negligible)
• Electrons:
– If it’s an atom, the protons and electrons must be
the SAME so that it is has a net charge of zero
(equal numbers of + and -)
– If it does NOT have an equal number of electrons, it
is not an atom, it is an ION. For each negative
charge, add an extra electron. For each positive
charge, subtract an electron (Don’t add a proton!!!
That changes the element!)
Learning Check 3a – Counting
Naturally occurring carbon consists of three
isotopes, 12C, 13C, and 14C. State the number of
protons, neutrons, and electrons in each of
these carbon atoms.
12C
6
13C
6
14C
6
#p+ _______
_______
_______
#no _______
_______
_______
#e- _______
_______
_______
Learning Check 3b
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14
2) 16
3) 34
B. Its mass number is
1) 14
2) 16
3) 34
C. The element is
1) Si
2) Ca
3) Se
D. Another isotope of this element is
1) 34X
2) 34X
3) 36X
16
14
14
IONS
• IONS are atoms or groups of atoms with a
positive or negative charge.
• Taking away an electron from an atom gives a
CATION with a positive charge
• Adding an electron to an atom gives an
ANION with a negative charge.
• To tell the difference between an atom and an
ion, look to see if there is a charge in the
superscript! Examples: Na+ Ca+2 I- O-2
Na
Ca
I
O
Forming Cations & Anions
A CATION forms
when an atom
loses one or
more electrons.
Mg -->
Mg2+
+ 2 e-
An ANION forms
when an atom
gains one or
more electrons
F + e- --> F-
PREDICTING ION CHARGES
In general
• metals (Mg) lose electrons ---> cations
• nonmetals (F) gain electrons ---> anions
Charges on Common Ions
-4 -3 -2 -1
+1
+2
+3
By losing or gaining e-, atom has same
number of e-’s as nearest Group 8A atom.
Learning Check 3c – Counting
State the number of protons, neutrons, and
electrons in each of these ions.
39
K+
19
16O -2
41Ca +2
8
20
#p+ ______
______
_______
#no ______
______
_______
#e- ______
______
_______
Learning Check 3d
Write the nuclear symbol form for the
following atoms or ions:
A. 8 p+, 8 n, 8 e-
___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 46 e-
___________
AVERAGE
ATOMIC
MASS
11B
10B
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value.
• Boron is 20% 10B and 80% 11B. That is, 11B is
80 percent abundant on earth.
• For boron atomic weight
= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
Isotopes & Average Atomic Mass
• Because of the existence of isotopes, the
mass of a collection of atoms has an average
value.
• 6Li = 7.5% abundant and 7Li = 92.5%
–Avg. Atomic mass of Li = ______________
•
28Si
= 92.23%, 29Si = 4.67%, 30Si = 3.10%
–Avg. Atomic mass of Si = ______________
Lesson 4
Organizing the Periodic Table
Essential Question
How are elements grouped in the
Periodic Table?
Objectives
• To identify similar properties of
elements in groups and periods.
Elements
Element- atoms having an identical
number of protons in each
nucleus. Elements cannot be
reduced to simpler substances by
normal chemical means.
• Elements are organized into the
Periodic Table of Elements by
their Atomic Number
• 1H
2He 3Li
4Be
5B
6C
7N
The Periodic Table
Periods in the Periodic Table
Groups in the Periodic Table
Elements in groups react in similar ways!
Regions of the Periodic Table
Group 1A: Alkali Metals
Reaction of
potassium + H2O
Cutting sodium metal
Group 2A: Alkaline Earth Metals
Magnesium
Magnesium
oxide
Group 7A: The Halogens
(salt makers)
F, Cl, Br, I, At
Group 8A: The Noble
(Inert) Gases
He, Ne, Ar, Kr, Xe, Rn
• Lighter than air
balloons
• “Neon” signs
• Very Unreactive
because they
have full electron
levels
XeOF4
Transition Elements
Lanthanides and actinides
Iron in air gives
iron(III) oxide
ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
Remember:
BrINClHOF
Hockey Stick and the Puck
These elements
only exist as
PAIRS. Note that
when they
combine to make
compounds, they
are no longer
elements so they
are no longer in
pairs!
Compounds
• Compounds are…
–Substances that are made from atoms of
two or more different elements chemically
bonded together.
–Ex: NaCl, CaCO3
Molecules
• Molecules are…
–Substances that are made from atoms of
two or more alike or different element
chemically bonded together.
–Ex: O2, H2 (diatomics), NaCl