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Balancing equations comes from the work of a French chem- ist, Antoine Lavoisier. In the 1700s, Lavoisier found that the total mass of the reactants was always the same as the total mass of the products. Lavoisier’s work led to the law of conservation of mass. This law states that mass is neither created nor destroyed in ordinary chemical and physi- cal changes. This law means that a chemical equation must show the same numbers and kinds of atoms on both sides of the arrow.

To balance an equation, you must use coefficients. A coefficient is a number that is placed in front of a chemical symbol or formula. For example, 2CO represents two carbon monoxide molecules. The number 2 is the coefficient.

For an equation to be balanced, all atoms must be counted. So, you must multiply the subscript of each element in a formula by the formula’s coefficient. For example, 2H2O contains a total of four hydrogen atoms and two oxygen atoms. Only coefficients—not subscripts—are changed when balancing equations. Changing the subscripts in the formula of a compound would change the compound.

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Chemical Formulas, Chemical Equations, Chemical Reactions,

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Chemical Formulas, Chemical Equations, Chemical Reactions,

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Review

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For Ionic Compounds

If the name of a compound contains the name of a metal and the name of a nonmetal, the compound is ionic. To write the formula for an ionic compound, make sure the compound’s charge is 0. In other words, the formula must have subscripts that cause the charges of the ions to cancel out. Figure 3 shows you how to write a chemical formula from the name of an ionic compound.

Ionic Compounds

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For Covalent Compounds

If you know the name of the covalent compound, you can often write the chemical formula for that compound. Covalent compounds are usually composed of two nonmetals. The names of many covalent compounds use prefixes. Each prefix represents a number, as shown in Table 1. The prefixes tell you how many atoms of each element are in a formula. Figure 2 shows you how to write a chemical formula from the name of a covalent compound.

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A chemical equation uses chemical symbols and formulas as a shortcut to describe a chemical reaction.

Parts of a Chemical Reaction

The starting materials in a chemical reaction are reactants.

The substances formed from a reaction are products.
In this example, carbon and oxygen are reactants. Carbon dioxide is the product.

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A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance. A chemical formula shows how many atoms of each kind are present in a molecule.

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A chemical bond is a force that holds two atoms together in a molecule. For a chemical reaction to take place, the original bonds must break and new bonds must form.

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Objectives:

Describe how chemical reactions produce new substances that have different chemical and physical properties.

Identify four signs that indicate that a chemical reaction might be taking place.

Explain what happens to chemical bonds during a chemical reaction.

Terms to Learn :
chemical reaction precipitate

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A chemical reaction is a process in which one or more substances change to make one or more new substances.

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An ionic bond is a bond that forms when electrons are transferred from one atom to another atom.

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A covalent bond forms when atoms share one or more pairs of electrons.
WATER

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Oxygen - Chlorine

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Sodium - Aluminum

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Sulphur - Magnesium

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Electrons in the outermost layer.

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Hydrogen molecule H₂

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How metals are good conductors of electricityt?

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How metals are good conductors of electricityt?

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Conductors & Non-Conductors | Properties of Matter | Chemistry | FuseSchool

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What is electricity? - Electricity Explained - (1)

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History and Facts

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The Periodic Table: Crash Course Chemistry #4

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The Periodic Table Song (2018 Update!) | SCIENCE SONGS

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Metalloids have some properties of metals and some properties of nonmetals

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Comparison Properties of Metals and Non-metals

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Comparison Properties of Metals and Non-metals

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Metals are:
Shiny
Ductile
Maleable
Good conductors or thermal energy
Good conductors of electricity.

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Notes:
Periodic means “happening at regular intervals.”
Dimitri Mendeleev found that the elements’ properties followed a pattern that repeated every seven elements.

His table became known as the periodic table of the elements.

The periodic law: periodic law states that the repeating chemical and physical properties of elements change periodically with the elements’ atomic numbers.

Each element has a chemical symbol.

Each horizontal row of elements (from left to right) on the periodic table is called a period.

Each vertical column of elements (from top to bottom) on the periodic table is called a group.
Elements in the same group often have similar chemical and physical properties. For this reason, a group is also called a family.

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Atoms, Elements, Isotops and The Periodic Table

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Atoms, Elements, Isotops and The Periodic Table

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Textbook

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Objectives