U2L6 - Interactions of Atoms

Unit 2 Lesson 6 Interactions of Atoms

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Indiana Standards


• 8.1.3 Explain how the arrangement of atoms and molecules determines chemical properties of substances.

• 8.1.4 Describe the structure of an atom and relate the arrangement of electrons to how that atom interacts with other atoms.

• 8.1.5 Explain that atoms join together to form molecules and compounds and illustrate with diagrams the relationship between atoms and compounds and/or molecules.


Indiana Standards


• 8.1.7 Explain that chemical changes occur when substances react and form one or more different products, whose physical and chemical properties are different from those of the reactants.

• 8.1.8 Demonstrate that in a chemical change, the total numbers of each kind of atom in the product are the same as in the reactants and that the total mass of the reacting system is conserved.

Breaking Up and Making Up


What happens to atoms during a chemical change?• During a chemical change, atoms are not created

or destroyed. Instead, the atoms are simply rearranged.

• The atoms that make up a substance are joined by chemical bonds. During a chemical change, chemical bonds are formed and broken. The result of a chemical change is different combinations of atoms joined by bonds.


What happens to atoms during a chemical change?• When the atoms in a substance are rearranged,

the identity of the substance changes. The new substance has different chemical properties.

• A molecule is a distinct group of atoms held together by chemical bonds. Different molecules have different chemical properties.



How are chemical changes described?

• A chemical equation can be used to describe a chemical change, or reaction.

• A chemical equation uses symbols to represent the various substances that interact during a reaction.




• In a chemical equation, each substance is represented by a chemical formula that describes the substance’s makeup in a shorthand way.

• The chemical formula for carbon dioxide is CO2. The letters C and O represent the elements carbon and oxygen. The 2 is a subscript that tells you that there are two oxygen atoms in a molecule of CO2.




C + O2 CO2

• In a chemical equation, the starting materials, or reactants, appear on the left side of the arrow.

• The substances formed in the reaction, the products, appear on the right side of the arrow.

• What are the reactants and products in this chemical equation?



A Balancing Act


How do chemical equations show the law of conservation of mass?• The law of conservation of mass states that matter

is neither created nor destroyed in ordinary physical and chemical changes.

• A balanced chemical equation shows the same numbers and kinds of atoms on both sides of the equation.


How do chemical equations show the law of conservation of mass?

2C + O2 2CO

• Coefficients are numbers placed in front of chemical formulas in order to balance an equation.

• In this balanced chemical equation, a coefficient of 2 appears in front of the C and the CO.

• This chemical equation shows two carbon atoms and two oxygen atoms on each side of the arrow.



Let’s Get Together


How is chemical bonding modeled?

• There are different ways of modeling an atom. The model you choose depends on how you will use the model.



• A type of atom model called a Bohr model shows electrons as dots arranged in rings around the nucleus.




• Bohr models are useful for making predictions about how atoms form and break bonds during chemical reactions.

• The rings in a Bohr model represent different energy levels. Each energy level can hold a different number of electrons.

• The first, innermost energy level can hold up to two electrons. The second energy level can hold up to eight electrons.




• The electrons in the outermost energy level of an atom are called valence electrons.

• Only valence electrons participate in chemical bonding. Other electrons in an atom do not.




• How many valence electrons are in this lithium atom?




• When an energy level of an atom contains the maximum number of electrons, the energy level is full.

• An atom with a full outermost energy level is stable and usually does not form bonds. This kind of atom is usually not reactive.




• An atom that does not have a full outermost energy level can form bonds in order to achieve a full outermost energy level.

• This kind of atom can form bonds by sharing electrons with other atoms or by transferring electrons between atoms.



U2L6 - Interactions of Atoms

Science

Transcript of U2L6 - Interactions of Atoms