Chemistry Unit Review

1
Chemistry Unit Review

• Answer Key

2
Structure of an atom

• Electron Negative
• Proton Positive
• Neutron Neutral

2. What element is this atom? How can you tell by
looking at the diagram? Lithium The element has
3 protons which is the same as the atomic number
on the periodic table.
3
Structure of an atom cont.

• 3. What is the mass of this atom? 7
• How can you tell by looking at the diagram?
  The mass of an atom is found by adding the
  protons and neutrons together. This atom has 3
  protons 4 neutrons.
• 4. Which subatomic particle has the smallest
  mass?
• electron
• 5. What happens to this atom when you
• a. Remove an electron? It becomes an ion(cation)
• b. Remove a neutron? It has less mass and is
  called an isotope
• c. Add a proton? It becomes Berylium
• 6. How could you change this atom into helium?
  You would have to remove 1 proton

4
Periodic table trends and organization

• 1. Why are He, Ar, and Kr all un-reactive with
  other elements? Their outer shells are either
  full or have 8 electrons making them very stable
• 2. Give a list of three elements you expect to
  have similar chemical properties, and explain
  why. Could be any 3 elements in a group(column)
  all have the same number of valence electrons
  giving them similar properties
• 3. What are valence electrons? The outermost
  shell of electrons can be 1 to 8 of them
• 4. How do valence electrons determine the
  chemical properties of an element? Explain why
  using at least two examples. Valence electrons
  are what determines the reactivity of an atom as
  well as what type of bond it is most likely to
  form. Ex Sodium has one valence e-, so it is
  very likely to react to get rid of this electron.
  Neon has 8 so it is very stable.

5
Periodic table trends and organization cont.
5. Fill out the following table.
Element Group Period Atomic Atomic Mass of Protons of Neutrons of Electrons Valence Electrons Energy Shells
Be 2A 2 4 9.012 4 5 4 2 2
Cl 17 3 17 35.45 17 18 17 7 3
Kr 18 4 36 83.798 36 48 36 8 4
6. Categorize these elements as either metals or
non-metals. Carbon Sodium Calcium Silver
Hydrogen Iron Oxygen Fluorine
Metals Non-metals
Sodium, Calcium, Silver, Iron Carbon, Hydrogen, Oxygen, Fluorine
6
Ions and isotopes

1. Fill out the table below for isotopes of carbon.

Isotope of Protons of Neutrons of Electrons Atomic Mass
Carbon-12 6 6 6 12
Carbon-13 6 7 6 13
Carbon-14 6 8 6 14
2. How do you change the charge of an atom? By
adding or taking away electrons from the outer
shell.
7
Chemical bonds

• Identify the following substances as either an
  element or a
• compound.

Substance Element or Compound?
NaOH Compound
CO Compound
Co Element
CuSO4 Compound
Cu Element
2. How many elements are in a molecule of CaSO4?
How many atoms total? 3 Elements and 6 total
atoms
8
Chemical bonds cont
3. What is the chemical formula for this
molecule? How do you know?
NO2 There are 2 atoms of oxygen
and 1 atom of
nitrogen. The
nitrogen comes first because it is
in
the group before oxygen.
4. Why do different atoms bond together to make
compounds? Atoms bond together to satisfy the
full outer shell or 8 valence electron rule
which makes them more stable. 5. Describe what
happens to valence electrons in ionic bonding.
In an ionic bond one atom gives up valence
electrons making it a positive cation while
the other takes in those valence electrons
making it a negative anion. 6. Why do negatively
charged and positively charged ions combine
to form compounds? The opposite charged atoms
are attracted to each other and they form a weak
bond.
9
Chemical bonds cont
7. Write the chemical formula for the following
compounds. Also, write the ions and their
charges for each compound.
Name Positive charged Ion (include the chemical symbol and charge) Negative charged Ion (Include the chemical symbol and charge) Chemical Formula
Ex Magnesium Iodide Mg2 2 I-1 MgI2
Potassium Bromide K1 Br-1 KBr
Calcium Chloride Ca2 Cl-1 CaCl2
Magnesium Oxide Mg2 O-2 MgO
8. Describe what happens to valence electrons in
covalent bonding. Valence electrons are
shared by each atom in a covalent bond.
10
Chemical bonds cont

• 9. Write the formula for a covalent bond between
  carbon and Chlorine.
• CCl4
• 10. Classify the bonding in each compound as
  covalent or ionic.
• Carbon dioxide (CO2) covalent
• Aluminum sulfide (Al2S3) ionic
• Silicon dioxide (SiO2) covalent
• Potassium bromide (KBr) ionic
• Sodium chloride (NaCl) ionic
• Magnesium oxide (MgO) ionic