Elements and Atoms

1
Table of Contents

• Elements and Atoms
• Atoms, Bonding, and the Periodic Table
• Ionic Bonds
• Covalent Bonds
• Bonding in Metals

2
The Building Blocks of Matter
- Elements and Atoms

• Matter may consist of elements, compounds, or
  mixtures.

3
Atomic Theory and Models
- Elements and Atoms

• Dalton thought that atoms were like smooth, hard
  balls that could not be broken into smaller
  pieces.

4
Atomic Theory and Models
- Elements and Atoms

• Thomson suggested that atoms had negatively
  charged electrons embedded in a positive sphere.

5
Atomic Theory and Models
- Elements and Atoms

• Rutherford was surprised that a few particles
  were deflected strongly. This led him to propose
  an atomic model with a positively charged nucleus.

6
Atomic Theory and Models
- Elements and Atoms

• Through the first part of the twentieth century,
  atomic models continued to change.

7
Outlining
- Elements and Atoms
Elements and Atoms

• The Building Blocks of Matter
• Elements, Compounds, and Mixtures
• Particles of Elements
• Atomic Theory and Models
• Daltons Atomic Theory
• Thomson and Smaller Parts of Atoms
• Rutherford and the Nucleus
• Bohrs Model
• A Cloud of Electrons
• The Modern Atomic Model

• As you read, make an outline about elements and
  atoms. Use the red headings for the main ideas
  and the blue headings for the supporting ideas.

8
More on Atomic Structure
- Elements and Atoms

• Click the PHSchool.com button for an
  activityabout atomic structure.

9
End of SectionElements and Atoms
10
Valence Electrons and Bonding
- Atoms, Bonding, and the Periodic Table

• The number of valence electrons in an atom of an
  element determines many properties of that
  element, including the ways in which the atom can
  bond with other atoms.

11
The Periodic Table
- Atoms, Bonding, and the Periodic Table

• Elements are organized into rows and columns
  based on their atomic number.

12
The Periodic Table
- Atoms, Bonding, and the Periodic Table

• As the number of protons (atomic number)
  increases, the number of electrons also
  increases. As a result, the properties of the
  elements change in a regular way across a period.

13
The Periodic Table
- Atoms, Bonding, and the Periodic Table

• The variety of colors in a neon sign results
  from passing an electric current through sealed
  glass tubes containing different noble gases.

14
Building Vocabulary
- Atoms, Bonding, and the Periodic Table

• After you read the section, reread the paragraphs
  that contain definitions of Key Terms. Use the
  information you have learned to write a
  definition of each Key Term in your own words.

Key Terms
Examples
valence electrons
Valence electrons are electrons that are of the
highest energy level and are held most loosely.
The atomic number of an element is the number of
protons in the nucleus of an atom.
A halogen is any element in Group 17, which
consists of elements with seven valence electrons.
electron dot diagram
The symbol for the element surrounded by dots
that stand for valence electrons is an electron
dot diagram.
A alkali metal is any element in Group 1, which
consists of elements with one valence electron.
A row of elements across the periodic table is
called a period.
chemical bond
A chemical bond is the force of attraction that
holds two atoms together as a result of the
rearrangement of electrons between them.
Elements in the same column are called a group or
family.
A noble gas is any element in Group 18, which
consists of elements with eight valence electrons.
symbol
Each element is represented by a symbol, usually
consisting of one or two letters.
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End of SectionAtoms, Bonding, and the Periodic
Table
16
Ions and Ionic Bonds
- Ionic Bonds

• You and a friend walk past a market that sells
  apples for 40 cents each and pears for 50 cents
  each. You have 45 cents and want an apple. Your
  friend also has 45 cents but wants a pear.

17
Ions and Ionic Bonds
- Ionic Bonds

• When an atom loses an electron, it loses a
  negative charge and become a positive ion. When
  an atom gains an electron, it gains a negative
  charge and becomes a negative ion.

18
Ions and Ionic Bonds
- Ionic Bonds

• Ions are atoms that have lost or gained electrons.

19
Ions and Ionic Bonds
- Ionic Bonds

• Ionic bonds form as a result of the attraction
  between positive and negative ions.

20
Properties of Ionic Compounds
- Ionic Bonds

• In general, ionic compounds are hard, brittle
  crystals that have high melting points. When
  dissolved in water or melted, they conduct
  electricity.

21
Previewing Visuals
- Ionic Bonds

• Before you read, preview Figure 17. Then write
  two questions that you have about the diagram in
  a graphic organizer like the one below. As you
  read, answer your questions.

Formation of an Ionic Bond
Q. What is an ionic bond?
A. An ionic bond is the attraction between two
oppositely charged ions.
Q. What is the overall charge on an ionic
compound?
A. Overall, an ionic compound is electrically
neutral.
22
Links on Ionic Compounds
- Ionic Bonds

• Click the SciLinks button for links on ionic
  compounds.

23
End of SectionIonic Bonds
24
How Covalent Bonds Form
- Covalent Bonds

• The force that holds atoms together in a covalent
  bond is the attraction of each atoms nucleus for
  the shared pair of electrons.

25
How Covalent Bonds Form
- Covalent Bonds

• The oxygen atom in water and the nitrogen atom in
  ammonia are each surrounded by eight electrons as
  a result of sharing electrons with hydrogen atoms.

26
How Covalent Bonds Form
- Covalent Bonds

• An oxygen molecule contains one double bond,
  while a carbon dioxide molecule has two double
  bonds. A nitrogen molecule contains one triple
  bond.

27
Comparing Molecular and Ionic Compounds
- Covalent Bonds

• The table compares the melting points and boiling
  points of a few molecular compounds and ionic
  compounds. Use the table to answer the following
  questions.

28
Comparing Molecular and Ionic Compounds
- Covalent Bonds

• Graphing
• Create a bar graph of just the melting points of
  these compounds. Arrange the bars in order of
  increasing melting point. The y-axis should start
  at 200ºC and go to 900ºC.

• Check that the graphs are correctly set up and
  labeled before students plot the data.

29
Comparing Molecular and Ionic Compounds
- Covalent Bonds

• Interpreting Data
• Describe what your graph reveals about the
  melting points of molecular compounds compared to
  those of ionic compounds.

• Melting points of molecular compounds are lower
  than those of ionic compounds.

30
Comparing Molecular and Ionic Compounds
- Covalent Bonds

• Inferring
• How can you account for the differences in
  melting points between molecular compounds and
  ionic compounds?

• Molecular compounds have weak attractive force
  between molecules, so less energy is needed to
  melt molecular compounds.

31
Comparing Molecular and Ionic Compounds
- Covalent Bonds

• Interpreting Data
• How do the boiling points of the molecular and
  ionic compounds compare?

• Boiling points of molecular compounds are lower
  than those of ionic compounds.

32
Comparing Molecular and Ionic Compounds
- Covalent Bonds

• Predicting
• Ammonias melting point is 78ºC and its boiling
  point is 34ºC. Is ammonia a molecular compound
  or an ionic compound? Explain.

• Students may predict that ammonia is a molecular
  compound because it has relatively low melting
  and boiling points.

33
Unequal Sharing of Electrons
- Covalent Bonds

• Fluorine forms a nonpolar bond with another
  fluorine atom. In hydrogen fluoride, fluorine
  attracts electrons more strongly than hydrogen
  does, so the bond formed is polar.

34
Unequal Sharing of Electrons
- Covalent Bonds

• A carbon dioxide molecule is a nonpolar molecule
  because of its straight-line shape. In contrast,
  a water molecule is a polar molecule because of
  its bent shape.

35
Asking Questions
- Covalent Bonds

• Before you read, preview the red headings. In a
  graphic organizer like the one below, ask a what
  or how question for each heading. As you read,
  write answers to your questions.

How do covalent bonds form?
Covalent bonds form when two atoms share
electrons.
What are molecular compounds?
Molecular compounds are compounds that contain
molecules bonded with covalent bonds.
How does unequal sharing of electrons affect the
atoms in molecular compounds?
Unequal sharing of electrons causes the bonded
atoms to have slight electrical charges.
36
Links on Molecular Compounds
- Covalent Bonds

• Click the SciLinks button for links on molecular
  compounds.

37
End of SectionCovalent Bonds
38
Metallic Bonding
- Bonding in Metals

• A metal crystal consists of positively charged
  metal ions embedded in a sea of valence
  electrons.

39
Metallic Properties
- Bonding in Metals

• The sea of electrons model of solid metals
  explains their ability to conduct heat and
  electricity, the ease with which they can be made
  to change shape, and their luster.

40
Relating Cause and Effect
- Bonding in Metals

• As you read, identify the properties of metals
  that result from metallic bonding. Write the
  information in a graphic organizer like the one
  below.

Effects
Electrical conductivity
Heat conductivity
Cause
Metallic bonding
Ductility
Malleability
Luster
41
Links on Metallic Bonding
- Bonding in Metals

• Click the SciLinks button for links on metallic
  bonding.

42
End of SectionBonding in Metals
43
Graphic Organizer

Polar Covalent Bond
Nonpolar Covalent Bond
Metallic Bond
Feature
Ionic Bond
Attraction between positive ions and surrounding
electrons.
Attraction between oppositely charged ions
How Bond Forms
Equal sharing of electrons
Unequal sharing of electrons
Charge on Bonded Atoms?
Yes, slightly positive or slightly negative
Yes positive or negative
Yes positive
No
H2O molecule (or other polar covalent molecule)
NaCl crystal (or other ionic compound)
Example
Calcium (or other metal)
O2 molecule
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End of SectionGraphic Organizer