7 th grade chemistry. elements and atoms what is chemistry? chemistry is the study of the properties...
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7th Grade Chemistry
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Elements and Atoms
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What is Chemistry?
• Chemistry is the study of the properties of matter and how matter changes
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What is Matter?
• Matter is anything that has mass and takes up space
What are some examples of objects that contain matter?
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What is an Element?
• An element is a substance that cannot be broken down into any other substance by chemical or physical means
What does that mean?
• Elements are the simplest substances
• What are some examples of elements?
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What is an Element?
What are some examples of elements?
• Oxygen
• Hydrogen
• Gold
• Silver ……..just to name a few
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How many elements are there?
• There are 118 known elements on the Earth.
What does that mean?
• Everything on the Earth is made of one or more of those 118 elements
• Elements of the periodic table song http://www.youtube.com/watch?v=zUDDiWtFtEM
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What is a compound?
• A Compound is a pure substance made of two or more elements
What are some examples of compounds?
• Water
• Carbon dioxide
• Salt
• Table sugar
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What is a compound?
• A compound and molecule are represented by a chemical formula which shows the element in the compound and the ratio.
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What is a chemical bond?
• A chemical bond is the force of attraction between two atoms, when they combine.
• Atoms combine to form larger particles called molecules
• A molecule is simply two or more atoms held together by a chemical bond
• Oxygen molecule
• http://www.brainpop.com/science/matterandchemistry/chemicalbonds/preview.weml
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What happens when two different atoms combine?
When elements are chemically combined, they form compounds having properties that are different from
those of the uncombined elements
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Example – salt (NaCl)
Sodium Properties
• Silver in color
• Solid
• Metal
• Very reactive
• Explodes when comes into contact with water.
Chlorine Properties
• Green
• Gas
• Low density
• Poisonous
• Very reactive
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Properties of Salt
• Solid
• White in color
• Not reactive
• Not poisonous
• Does not explode when coming into contact with water
• Soluble
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What is a mixture?
• A mixture is made of two or more substances—element, compound, or both– that are in the same place but ARE NOT chemically combined.
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What is a homogeneous mixture?
• A homogeneous mixture is a mixture in which the parts are so evenly mixed you can not tell the difference between them.
• A solution is an example of a homogeneous mixture. It is formed when one substance is dissolved into another.
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What is a heterogeneous mixture?
• In a heterogeneous mixture you can see the different parts
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How is a mixture different from a compound?
• Each substance in a mixture keeps its individual properties. Also the parts are not combined in a set ratio.
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Atoms, Bonding, and the Periodic Table
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What is an atom?
• An atom is the basic particle from which all elements are made
• Atoms make up all the elements
• Are the smallest pieces that retain physical and chemical properties
• “building blocks” of matter
• http://www.youtube.com/watch?v=cuXxSQEYDR8
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What are subatomic particles?
• An atom consists of a nucleus surrounded by one or more electrons.
• Neutron found in the nucleus of an atom (has no charge)
• Protons found in the nucleus, have a positive electric charge (+)
• Electrons move rapidly around the nucleus and have a negative charge (e-)
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What is a cloud of electrons??
• An atom has a positive center known as the nucleus surrounded by a “cloud” of negative charge.
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What is a cloud of electron?
• Most of the atom’s volume is the space in which electrons move.
• The space is huge compared to the amount of space taken by the nucleus.
• It symbolizes where electrons are LIKELY to be.
• An electrons movement is related to its energy level, or the specific amount of energy that it has.
• http://www.brainpop.com/science/matterandchemistry/atomicmodel/
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Comparing Particle Size
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Valance Electrons and Bonding
• An atom’s valance electrons are those that have the highest energy levels and are held most loosely.
• The number of valance electrons determine many properties of that element, including the ways in which the atom combines with other atoms
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What is the periodic table?
• The periodic table is a system used worldwide for organizing elements into categories
• http://www.brainpop.com/science/matterandchemistry/periodictableofelements/
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Organizing the Elements
• Each square on the periodic table is representing one of the known elements that make up all matter on Earth.
• Each element is represented by a symbol usually consisting of one or two letters
• Look at figure 10 on page 14
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Organizing the elements
• The atomic number of an element is the number of protons in the nucleus of an atom.
• As you look at the elements from left to right on the periodic table, what do you notice about the atomic number of the elements?
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Finding Data on Elements
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Finding Data on the periodic table
• In order to find the out how many subatomic particles an atom of a particular element has YOU MUST USE THE PERIODIC TABLE.
• The periodic table purpose is to help you understand properties of the elements without having to memorize them for 118 elements
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HELPFUL HINTS TO DETERMINE THE NUMBER OF SUBATOMIC PARTICLES
• The atomic number of an ATOM = the number of electrons
• The atomic number of an ATOM = the number of protons
• The atomic weight – atomic number = the number of neutrons
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Organization of the Periodic Table
• Remember the periodic table is arranged by atomic number.
• Atomic numbers as they increase from left to right, and read across each row.
• The Properties of an element can be predicated from its location in the periodic table.
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Periods
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Periods
• The table is arranged in horizontal rows called periods
• A period contains different elements that have different properties
• As you move from left to right in a period the properties change in pattern
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Groups
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Groups
• The modern period periodic table has 7 periods which form 18 vertical columns.
• The elements in a columns are called a group
• The groups are number from 1-18 going from left to right.
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Group
• Most groups are named for the first element in the group.
• Elements in each group have similar properties and react in similar ways.
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How the periodic table works
• The periodic table is based on the structure of atoms, especially the arrangement of the electrons.
• As the number of protons – or atomic number– increases, the number of electrons also increase. As a result, the properties of the element change in a regular way across a period.
• What do you notice about figure 11?
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How the periodic table works
• Except for period 1, a period ends when the number of valance electrons reaches eight
• THIS REPEATING PATTERN MEANS THAT ELEMENTS WITHIN THE SAME GROUP ALWAYS HAVE THE SAME NUMBER OF VALANCE ELECTRONS.
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Electron Dot Diagram
• Each element has a specific number of valance electrons ranging from 1-8
• An electron dot diagram is a way to show the number of electrons in the element.
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Bohr’s Diagram
• To display the entire atom you will use Bohr’s diagram
• Each circle represent an energy level.
• The farther away from the nucleus the more energy the electron has
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Chemical formulas and names
• Compounds can be represented by chemical formulas
• A chemical formula is a combination of symbols that shows the ratio of elements in a compound.
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Chemical formulas and names
• A subscript tells you the ratio of the elements in the compound.
• For every one hydrogen there are two oxygen atoms
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Observing Chemical Change
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What are the two types of properties?
• Physical properties
• chemical properties
What is a physical property?
• Physical property - is a characteristic of a pure substance that can be observed without changing it into another substance
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Types of physical properties
• density
• melting point
• boiling point
• solubility
• texture
• color
• odor
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What are the two types of properties?
• What is a chemical property?
• Chemical property – is a characteristic of a pure substance that describes its ability to change into a different substance
Types of chemical property
• Ability to react
• Flammability
• Corrosiveness
• Tarnishing
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What is the difference between a physical and a chemical change?
http://www.brainpop.com/science/matterandchemistry/propertychanges/
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What is a physical change?
• A physical change is any change that alters the appearance of matter but does not any change any substance into another substance.
• In other words, a physical change only changes what an object looks like.
• What some examples of a physical change?
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Physical Change
• A substance that undergoes a physical change is still the same substance after the change
• The substance still has the same properties
• A physical change has occurred when:
a. A change in the state of matter has occurred
b. A change in the shape or form occurs
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What is a chemical change?
• A change in matter that produces one or more new substances is called a chemical change or chemical reaction
• Unlike physical change, a chemical change produces substance with properties that are different from the original substance.
• What are some examples of a chemical change?
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Examples of a chemical change
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Chemical changes
• Chemical changes occur when bonds break and new ones form.
• As a result the new substances that are produced will have different physical and chemical properties than the original substances.
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Evidence for chemical reactions
• Chemical reactions involve two main kinds of changes that you can observe – formation of new substances and a change in energy.
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Formation of a new substance = new properties
• Changes in properties result when a new substance has been formed.
• Things to look for:
• Color change
• A solid may appear when two liquids are combined, also known as a precipitate.
• Gas is produced from combined solids or liquids
• Formation of bubbles
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How do you describe a chemical reaction?
A chemical equation
• A chemical equation is a short easy way to show a chemical reaction using symbols instead of words.
• Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction
• http://www.brainpop.com/science/matterandchemistry/chemicalequations/preview.weml
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Formulas in equations
• A chemical formula is a combination of symbols that represents the elements in a compound.
• The formula for carbon dioxide is above. This tells us that in every molecule there are two oxygen atoms and one carbon atom
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Structure of an Equation
• All chemical equations have a common structure
• Every equation tells what substances that you start with and the substance that you end with in a chemical reaction.
• Reactants = substances that you start with at the beginning of a reaction
• Products = substances that you end with after a reaction has occurred
• Subscript = the number in a chemical formula that tells the number of atoms in a molecule
• Coefficient = is the number placed in front of a chemical formula in an equation, it tells you how many atoms or molecules there are
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Changes in energy
• A change in energy occurs during a chemical reaction
• As matter changes it can either absorb or release energy.
• An endothermic reaction is a reaction in which energy is absorbed
• TEMPERATURE DECREASES!!!
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Changes in energy
• An exothermic reaction is a reaction that release energy
• TEMPERATURE INCREASES
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What is conservation of mass?
• The fact that matter is not created nor destroyed in any chemical or physical change is called The law of conservation of mass
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• No mass is lost, because during a chemical change, atoms are not lost or gained, only rearranged
• http://www.brainpop.com/science/matterandchemistry/conservationofmass/