Transcript
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 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
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