Atoms and Bonding - Elements and Atoms The Building Blocks of Matter Matter may consist of elements, compounds, or mixtures.

Atoms and Bonding - Elements and Atoms

The Building Blocks of Matter

Matter may consist of elements, compounds, or mixtures.

Atoms and Bonding - Elements and Atoms

Atomic Theory and Models

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

Atoms and Bonding - Elements and Atoms

Atomic Theory and Models

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

Atoms and Bonding - Elements and Atoms

Atomic Theory and Models

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

Atoms and Bonding - Elements and Atoms

Atomic Theory and Models

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

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

Valence Electrons and Bonding

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.

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

The Periodic Table

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

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

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.

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

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.

Atoms and Bonding

Building VocabularyAfter 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.

- Atoms, Bonding, and the Periodic Table

Key Terms: Examples:

valence electrons Valence electrons are electrons that are of the highest energy level and are held most loosely.

electron dot diagram The symbol for the element surrounded by dots that stand for valence electrons is an electron dot diagram.

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.

symbol Each element is represented by a symbol, usually consisting of one or two letters.

Key Terms: Examples:

atomic number

period

groupfamily

noble gas

The atomic number of an element is the number of protons in the nucleus of an atom.

A row of elements across the periodic table is called a period.

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.

Key Terms: Examples:

halogen

alkali metal

A halogen is any element in Group 17, which consists of elements with seven valence electrons.

A alkali metal is any element in Group 1, which consists of elements with one valence electron.

Atoms and Bonding - Ionic Bonds

Ions and 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.

Atoms and Bonding - Ionic Bonds

Ions and 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.

Atoms and Bonding - Ionic Bonds

Ions and Ionic Bonds

Ions are atoms that have lost or gained electrons.

Atoms and Bonding - Ionic Bonds

Ions and Ionic Bonds

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

Atoms and Bonding - Ionic Bonds

Properties of Ionic Compounds

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

Atoms and Bonding

Previewing VisualsBefore 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.

- Ionic Bonds

Atoms and Bonding

Salt

Click the Video button to watch a movie about salt.

- Ionic Bonds

Atoms and Bonding - Covalent Bonds

How Covalent Bonds Form

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

Atoms and Bonding - Covalent Bonds

How Covalent Bonds Form

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.

Atoms and Bonding - Covalent Bonds

How Covalent Bonds Form

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

Atoms and Bonding

Comparing Molecular and Ionic Compounds

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.

- Covalent Bonds

Atoms and Bonding

Comparing Molecular and Ionic Compounds

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

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.

- Covalent Bonds

Atoms and Bonding

Comparing Molecular and Ionic Compounds

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

Interpreting Data:

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

- Covalent Bonds

Atoms and Bonding

Comparing Molecular and Ionic Compounds

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

Inferring:

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

- Covalent Bonds

Atoms and Bonding

Comparing Molecular and Ionic Compounds

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

Interpreting Data:

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

- Covalent Bonds

Atoms and Bonding - Covalent Bonds

Unequal Sharing of Electrons

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.

Atoms and Bonding - Covalent Bonds

Unequal Sharing of Electrons

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.

Atoms and Bonding

Question Answer

Asking QuestionsBefore 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.

- Covalent Bonds

Atoms and Bonding - Bonding in Metals

Metallic Bonding

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

Atoms and Bonding - Bonding in Metals

Metallic Properties

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.

Atoms and Bonding

Relating Cause and EffectAs you read, identify the properties of metals that result from metallic bonding. Write the information in a graphic organizer like the one below.

Metallic bonding

Electrical conductivity

Heat conductivity

Ductility

Malleability

Luster

Cause

Effects

- Bonding in Metals

Atoms and Bonding

Graphic Organizer

Attraction between oppositely charged ions

Feature Ionic BondPolar Covalent Bond

Nonpolar Covalent Bond

Metallic Bond

How Bond Forms

Charge on Bonded Atoms?

Example

Unequal sharing of electrons

Yes; positive or negative Yes; positive

O2 molecule

Equal sharing of electrons

Attraction between positive ions and surrounding electrons.

Yes, slightly positive or slightly negative

No

NaCl crystal (or other ionic compound)

H2O molecule (or other polar covalent molecule)

Calcium (or other metal)