Transcript Chemical Bonding

Chapter 13
Chemical Bonding
Section 1: Objectives
 Describe chemical bonding.
 Identify the number of valence electrons.
 Predict whether an atom is likely to form
bonds.
Combining Atoms
 All substances are made up of atoms of
one or more of the elements.
 Chemical bonding: joining of atoms to
form new substances
 Chemical bond: an interaction that
holds 2 atoms together
Combining Atoms
 To understand how atoms bond, you
need to determine the # of electrons.
 Atomic # = # of protons
 What else do we know about the atomic
#?
Combining Atoms
 Electrons are arranged in levels.
 Not all electrons in an atom make bonds.
 Most atoms form bonds with valence
electrons.
Forming a Compound:
Example # 1 (K and F)
Combining Atoms
 Elements are grouped based on similar
properties.
 Within a group, atoms have the same
number of valence electrons.
 Group numbers help you determine the
number of valence electrons.
Combining Atoms
 Not all atoms bond the same way.
 The # of electrons in the outermost shell
determines if an atom will bond.
 What group of atoms is not likely to form
bonds? Why?
 What group/groups are more likely to form
bonds? Why?
Forming a Compound: Example #
2 (H, He, C, and Ne)
Combining Atoms
 Atoms bond by gaining, losing, and
sharing electrons.
 Their goal is to fill the outermost energy
level.
 A filled outermost level contains ____
electrons.
Combining Atoms
 Not all atoms need 8 electrons to have a
full outer level.
 The outermost energy level of helium
only has 2 electrons and it is full.
 How is this true for helium?
Ch. 13 Section 1: Review
 1) What are all substances made up of?
 2) Why is understanding the number of
electrons in an element important?
 3) How are elements grouped?
 4)T/F All atoms bond the same way.
 5) How do atoms bond?
 6)How do most atoms form bonds?
 7) T/F All electrons in an atom can make
bonds.
Section 2: Objectives
 Explain how ionic bonds form.
 Describe how positive ions form.
 Describe how negative ions form.
 Explain why ionic compounds are
neutral.
Chemical Bonds
 Ionic bond: bond that is formed when
electrons are transferred from one atom
to another
 These form so that the outermost energy
level is filled.
 What does the name of the bond sound
like?
Chemical Bonds
 An atom is neutral because the number of
electrons equals the number of protons.
 The transfer of electrons causes the number of
electrons and the charge to change.
 Ion: charged particle that forms when an atom
or group of atoms gains or loses one or more
electrons
Chemical Bonds
 Most metals have few valence electrons.
 Metal atoms tend to lose their valence
electrons and form positive ions.
Chemical Bonds
 Energy is needed to pull electrons away
from atoms.
 Only a small amount of energy is needed
to take electrons from metal atoms.
 That is why elements in Groups 1 and 2
react easily.
Chemical Bonds
 Some atoms gain electrons from other
atoms during chemical changes.
 These atoms then have more electrons
than protons.
 What does this mean for their charge?
Chemical Bonds
 The outermost energy level of a non-
metal is almost full.
 They only need a few electrons in order
to be full.
 Nonmetals tend to gain electrons from
other atoms.
Chemical Bonds
 Energy is given off when non-metals
gain electrons.
 Group 17 elements give off the most
energy when they gain an electron.
Chemical Bonds
 When ionic compounds form, the # of electrons
lost by the metal atoms equals the number
gained by the non-metal atoms.
 The ions that bond are charged, but the
compound is neutral.
 Crystal lattice: regular pattern in which a
crystal is arranged
Chemical Bonds
 Most things, such as water and sugar,
are held together by covalent bonds.
 Low melting and boiling points.
 Brittle in solid state.
Chemical Bonds
 Covalent bond: formed when atoms share one
or more pairs of electrons
 In non-metals, atoms don’t donate electrons to
form a bond with another non-metal because it
requires too much energy.
 Non-metals share electrons (covalent bonds).
Chemical Bonds
 A molecule consists of 2 or more atoms
combined in a definite ratio.
 Most atoms are composed of molecules
of 2 or more different elements.
Chemical Bonds
 One way to represent atoms is to draw
an electron dot diagram.
 E.D. diagrams help you predict how
atoms might bond.
 To draw: write the element symbol and
draw dots for every V.E.