Mod3

Periodic Table of the Elements

Periodic Table: Basic Concepts3

Periodic Table

• Atomic number = the number of protons

• Each element has a specific number of

protons which makes it that element

• Electrons: each element initially has the

same number as protons.

• Electrons: are found in energy levels

around the nucleus

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Periodic Table

• Electrons: 1st energy level holds 2

electrons (e-). The rest of the energy

levels want 8 e-.

• Electrons: the last energy level is the

important one. Will give up or take e- to

obtain the magic number 8.

• The periodic table columns (1-18) tell you

how many e- are in the last energy level.

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Periodic Table

• Elements will either give up or take e- to

obtain stability (8)

• Elements on the left side of the table tend

to give up e-’s and elements on the right

side of the table tend to take e-’s.

• Column 18 elements have 8 in their last

energy level.

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Relationship of the Periodic

Table to Atomic Structure

Periodic Table: Basic Concepts3

Electrons in Energy Levels—Group 16

Periodic Table: Basic Concepts3

Electrons in Energy Level

You can also use the periodic table as a tool to

predict the number of valence electrons in

any atom in Groups

1, 2, 13, 14, 15, 16, 17, and 18.

The electrons in the outermost energy level are

called valence electrons.

All atoms in Group 1, like hydrogen, have one

valence electron. Likewise, atoms in Group 2

have two valence electrons.

Periodic Table: Basic Concepts3

Electrons in Energy Level

An oxygen atom has eight electrons. Two of

these fill the first energy level, and the

remaining six are in the second energy level.

Atomic Structure: Basic Concepts3

Formation of compounds

• Na (Sodium) is in column 1 and has 1

valence e-. It will give up this e- because

the energy level below it has 8.

• Cl (Chlorine) is in column 17 and has 7

valence e-’s. It will gain 1 e- to have 8.

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Electrons Can Be Transferred

Formation of Compounds: Basic Concepts

3

• Because the chlorine atom now has an extra electron, it has a negative charge.

• Also, because sodium lost an electron, it now has an unbalanced proton in the nucleus and therefore has a positive charge.

Formation of Compounds: Basic Concepts

3

• By this method, each atom achieves a stable noble gas configuration.

• The oxygen, by sharing two electrons with two hydrogens, claims a stable octet in its outer level.

Formation of Water by Electron Sharing

• Ionic bonding: oppositely charged

• Covalent bonding: share e-

3Bonding and Polarity

• Requirement:

• For each element, hydrogen, carbon, potassium, oxygen, and sodium, determine the following:

• a. Does it bond ionically or covalently?

• b. How many energy levels does it have?

• c. How many valence electrons does it have?

3Chemistry

Scientific Methods

• Often, a scientist will begin with qualitativedata—information that describes color, odor, shape, or some other physical characteristic that relates to the five senses.

• Chemists also use numerical quantitative data.

4Chemistry and Matter: Additional Concepts

• A hypothesis is a possible explanation for what has been observed.

• An experiment is a set of controlled observations that test a hypothesis.

Scientific Methods

• The variable that is changed in an experiment is called the independent variable.

• The variable that you watch to see how it changes as a result of your changes to the independent variable is called the dependent variable.

4Chemistry and Matter: Additional Concepts

Scientific Methods

• Many experiments also include a control, which is a standard for comparison.

• A conclusion is a judgment based on the data obtained in the experiment.

• If data support a hypothesis, the hypothesis is tentatively affirmed. Hypotheses are never proven; they are always subject to additional research.

4Chemistry and Matter: Additional Concepts

Scientific Methods

• Over time, data from many experiments can be used to form a visual, verbal, and/or mathematical explanation—called a model—of the phenomenon being studied.

4Chemistry and Matter: Additional Concepts

• A theory is an explanation that has been supported by many experiments.

• Theories are always subject to new experimental data and are modified to include new data.

Scientific Methods

• A scientific lawdescribes a relationship in nature that is supported by many experiments and for which no exception has been found.

4Chemistry and Matter: Additional Concepts

Scientific Research

• Pure research is done to gain knowledge for the sake of knowledge itself.

• Applied research is undertaken to solve a specific problem.

4Chemistry and Matter: Additional Concepts

Additional Assessment Questions

Identify the dependent variable and the

independent variable in the following

experiments.

Question 1 4

A student tests the ability of a given chemical

to dissolve in water at three different

temperatures.

independent variable:

dependent variable:

Answer 1a

Question 1a 4

Additional Assessment Questions

A farmer compares how his crops grow with

and without phosphorous fertilizers.

independent variable:

dependent variable:

Answer 1b

Question 1b 4

Additional Assessment Questions

Classify each kind of research as either pure

or applied.

Question 24

Additional Assessment Questions

A scientist studies plants in a rain forest in

search of chemicals that might be used to treat

AIDS.

Answer 2a

Question 2a 4

Additional Assessment Questions

A researcher studies the effects of hormones

on the brain of a worm.

Answer 2b

Question 2b 4

Additional Assessment Questions

A researcher tries to develop cleaner burning

fuels to help reduce air pollution.

Answer 2c

Question 2c 4

Additional Assessment Questions