PS%20101

1
PS 101

• Kim Cohn
• Email address
• Kcohn_at_academic.csubak.edu

2
5th Grade Standards 1

• Students know that during chemical reactions the
  atoms in the reactants rearrange to form products
  with different properties.
• Students know all matter is made up of atoms.
• Students know the properties of metals.
• Students know each element is made up of one kind
  of atom and that the elements are organized in
  the periodic table by their chemical properties.

3
Symbols to Memorize

• Sodium, Na.
• Iron, Fe
• Potassium, K
• Gold, Au
• Silver, Ag
• Lead, Pb
• Mercury, Hg

4
Demo

• Here is a demonstration of a reaction of an
  active metal with water.

Na (s)

H2O (l)
NaOH (aq)

H2 (g)
5
Metals and Alloys

• The symbol for sodium is Na.
• Na, a metal, has (how many?) electrons.
• The nearest inert gas has (how many?) electrons.
• To attain the nearest inert gas structure Na must
  (gain, lose) (how many?) electrons?
• One of the ways Na can do this is by sharing
  electrons with other sodium ions.

6
Metals and Alloys 2

• Here is a description of a metal.
• The Na atoms are arranged in a sea of
  electrons.
• No single electron belongs to a single Na atom.
• Explains properties of Metals

7
Metals and Alloys 3

• Here is a description of a alloy.
• Some Na atoms are replaced with K atoms.
• No single electron belongs to either a Na or K
  atom.

8
Ionic Bonds 1

• When an atom loses or gains an electron it
  becomes and ion.
• F as an atom has 9 electrons and 9 protons.
• To attain the nearest inert gas structure it must
  (gain, lose) (how many) electrons?
• Thus F turns into F-
• Na turns into
• Na

9
Ionic Bonds 2

• Therefore the atoms Na and F may be transformed
  into the ions by gaining or losing electrons.
• Na and F-
• Because these ions have opposite charges they
  will be held together to form the compound.
• NaF which is neutral.

10
Ionic Bonds 3

• Cl as an atom has 17 electrons.
• To attain the nearest inert gas structure it must
  (gain, lose) (how many) electrons?
• Thus Cl turns into Cl-
• Ca turns into
• Ca2
• The formula is CaCl2

11
Ionic Bonds 4

• First put the charges that you calculate above
  the ions.
• In this case 1 for Cl and 2 for Ca.
• Next cross the numbers as shown.
• The formula is CaCl2

2
-1
Ca
Cl
1
2
12
Ionic Bonds 5

• The positive and negative charges are arranged in
  an orderly way.
• Here is CsCl.
• See page 409 for NaCl
• These are ionic crystals.

13
Ionic Bonds 6 - Demo

• The light bulb will light when the circuit is
  completed
• What happens with NaCl?
• This is because the ions Na and Cl- carry the
  current.

14
Covalent Bonds

• When non-metals interact they often share
  electrons.
• Cl is an atom with 17 electrons.
• To attain the nearest inert gas structure it must
  (gain, lose) (how many) electrons?
• It can do this by sharing an electron with
  another Cl atom.

15
Covalent Bonds 2

• The Cl on the left has seven electrons in its
  outer shell, as does the one on the right.
• They can both attain an inert gas structure by
  sharing electrons.

16
Covalent Bonds 3

• Now both Cl atoms have eight electrons in their
  outer shell.
• Cl is found in nature as Cl2
• H is found in nature as H2

17
Covalent Bonds 4

• In the same way one oxygen atom with 6 electrons
  in the outer shell will combine with 2 hydrogen
  atoms that each have one electon in their shell
  to form water.

18
Covalent Bonds 5

• One oxygen atom with 6 electrons in the outer
  shell will combine with another O atom that has 6
  electron.
• Notice there are four electrons that are shared.

19
Covalent Bonds 6

• Pairs of electrons are usually shown as a line.
• The bond in O2 is usually shown as you see on the
  left.
• The four electrons that make up the two shared
  pairs are shown as two lines.

OO
20
Covalent Bonds 7

• Metal atoms exist in sea of electrons.
• In ionic bonds between a metal and a non-metal
  the metal gives up electrons and becomes
  positive, the non-metal gains electrons and
  becomes negative.
• Covalent bonds between two non-metals form by
  each atom sharing electrons with other atom(s).

21
Covalent Bonds 8 - Demo

• The light bulb will light when the circuit is
  completed
• What happened with NaCl?
• Sugar contains only covalent bonds.
• What will happen with sugar?

22
Covalent Bond Polarity 1

• When the two atoms are the same in a covalent
  bond the electrons are shared equally.
• For example, O2.

• OO

23
Covalent Bond Polarity 2

• When the two atoms are the different one of the
  atoms may have more of the electron density than
  another.
• For example, HF.
• The symbol ? means slightly positive.

• H?- F?-

24
Covalent Bond Polarity 3

• When the two atoms are the different one of the
  atoms may have much more of the electron density
  than another.
• For example, CsF.
• The symbol ? has been replaced by the sign
  indicating all of the extra electron on Cs is
  lost.

• Cs F-

25
Covalent Bond Polarity 4

• As is often the case there is no abrupt change
  from an ionic compound to a covalent one.
• All compounds are, at least to some extent,
  covalent.

26
Page 387 The Periodic Table
27
Covalent Bond Polarity 5

• Elements in the lower left like to lose
  electrons.
• Elements in the upper right like to gain
  electrons.

28
Covalent Bond Polarity 6

• Arrange the bonds on the left in order of
  increasing ionic character.
• OO is the least ionic.
• FS is the most ionic.
• OO is 100 covalent.

• As-S

O-O
F-S