The Structure of Atoms
Chapter 4 Section 2
Standards
• Standard 1: Matter
• #2 Describe the structure and
arrangement of atomic particles.
Objectives
• List differences between protons, neutrons, and
•
•
•
•
•
•
electrons
Explain what is unique about atoms and how ions
are formed
Tell how many protons, neutrons and electrons are
in an atom
Define isotopes and explain why they have
different atomic masses
Explain how the mole is used in chemistry
Convert between moles and grams
Calculate molar mass of compounds
The GREAT Trio
Objective 1: List differences
between protons, neutrons,
and electrons
Atoms are made of three major subatomic particles
• These are distinguished by mass, charge, and
location
Particle
Charge
Location
Mass (kg)
Proton
Positive
Nucleus
1.67 × 10-27
Neutron
Neutral
Nucleus
1.67 × 10-27
Negative
Electron
Cloud
9.11 × 10-31
Electron
Unique is the Way!!
Objective 2: Explain what is
unique about atoms and
how ions are formed
• All elements have a unique number of protons
•
Defines the element
• IF an atom has equal numbers of protons and electrons
the atom is
•
NEUTRAL!!
•
A negative ION – aNion!
•
A positive ION - ca+ion
• IF the atom has more electrons than protons the atom is
• IF the atom has more protons than electrons the atom is
• Three forces hold atoms together
•
Weak nuclear, strong nuclear, and electromagnetic!
Some ImPoRtAnT NuMbErS!!
• Atomic Number
Objective 3: Tell how many protons,
neutrons and electrons are in an atom
• Tells how many PROTONS are in the nucleus
• Tells how many ELECTRONS in a neutral atom
• Designated by A
• So…What is A for Carbon?? Hydrogen??
• Mass Number
• Equals the number of PROTONS + NEUTRONS
• Designated by M
• Atoms of each element have the same number
of protons, but can have different numbers of
neutrons as well as electrons!!
So…What BOUt the NEUTRON!!
• Symbols for the elements are usually written in
the form of
• M= mass #
M
• A= atomic #
A
Sm
Objective 3: Tell how many protons,
neutrons and electrons are in an atom
• Sm = Symbol of element
• Getting # of neutrons is simple..
• All we do is subtract M from A
• How do we know how many protons and
electrons are in the atom?
• LOOK at ATOMIC NUMBER!
•
•
For PROTONS and ELECTRONS in a NEUTRAL atom!
For ions ELECTRONS are found by subtracting (cation) or
adding (anion) the CHARGE from/to the atomic number
• Example…uranium-235
235
92
U
Weirdo Atoms…
• IsOtOpEs
Objective 4: Define isotopes
and explain how they make up
the atomic mass of an element
• Element with same # of protons but DIFFERENT
number of NEUTRONS
• These have different masses than the other atoms of a
particular element
• Their chemical and physical properties do NOT change
• Written as name of element – mass number
• Example – Uranium 235
• Hydrogen has 3 isotopes with DIFFERENT names!
•
•
•
Hydrogen – 1 (Hydrogen)
Hydrogen – 2 (Deuterium)
Hyrdrogen – 3 (Tritium)
• How many protons does each isotope of hydrogen have?
• How many neutrons does each isotope of hydrogen have?
Atomic Mass…
Objective 4: Define isotopes
and explain how they make up
the atomic mass of an element
• Atomic masses are weighted average
• It’s the average of the masses of all the
isotopes of an element
• Unit is the unified atomic mass unit (u)
•
•
Based on carbon – 12 (1/12 the mass of carbon – 12)
Makes working with small masses EASIER!
• We can find the most common isotope of
an element by looking at the atomic mass
• We just round the atomic mass!
Moles and Counting
Objective 5: Explain how the
mole is used in chemistry
• Because chemists deal with LARGE #s of small
particles
• They use a very LARGE counting unit called the mole
• 1 mole = 602, 213, 670, 000, 000, 000, 000, 000
particles
• This number is usually written as 6.022 × 1023
particles/mole
• Usually called Avogadro’s number
• Moles and grams are related!!
• The mass of one mole of a substance is called the molar
mass!
• Equals the atomic mass expressed in g/mol
•
Ex. 1 mole of carbon-12 = 12.00 g!! Also expressed as 12.00
g/mol
Compounds Have Molar
Masses TOO!!
• All we have to do is add up the
•
molar masses of the atoms
combined in the compound!
Must know number of atoms as
well as their masses!
• If there are SUBSCRIPTS by the
• Ex:
element you MULTIPLY the
subscript by the molar mass of
the element!
• What is the molar mass of
water?
• What is the molar mass of
carbon dioxide (CO2)
Objective 6: Calculate the
molar masses of compounds
Objective 7: Convert between
moles and grams
We Can Convert Between Moles and Grams!!
• Molar Masses help us to convert (change)
• Moles into grams or grams into moles!
• How to convert grams into moles
• Divide by molar mass!
• How to convert moles into grams
• Multiply by molar mass!
• Examples:
• What is the mass in grams of 5.50 mol of iron?
• How many moles are in 5.47 g of fluorine?
T – Charts for Converting!
• Moles to grams
Given
Moles
Unknown
Molar mass (g)
Moles
• Grams to moles:
Given
Grams
Unknown
Moles
Molar mass (g)