ENTRY QUIZ DESCRIBE BORON and BORON GROUP WHAT IS ELEMENT FOR TODAY? WHAT PROPERTIES DO YOU EXPECT? IS IT METAL? IS IT MAGNETIC?

Phosphorus P Atomic number 15 Atomic weight 30.97 NonMetal 15th ELEMENT Phosphorus P Atomic number 15 Atomic weight 30.97 NonMetal 15p, 15e, 16n

Chemical Formulas and Equations

The products of chemical research have substantially increased food supplies but have also increased the possibilities of pollution. Balancing the benefits and hazards of the use of chemicals requires a knowledge of chemistry and a knowledge of the alternatives.

Chemical Formulas

Introduction Empirical formula Molecular Formula Structural Formula The simplest whole number ratio of elements in a compound Ionic compounds are always shown as empirical formulas. Molecular Formula The actual numbers of atoms in a molecule. Structural Formula Show the relative arrangements of atoms in molecule

The name, molecular formula, sketch, and structural formula of some common molecules. Compare the kinds and numbers of atoms making up each molecule in the sketch to the molecular formula.

If you know the name of an ingredient, you can write a chemical formula, and the percent composition of a particular substance can be calculated from the formula. This can be useful information for consumer decisions.

Molecular and formula weights The formula weight of a compound is the sum of all of the atomic weights of the atoms in a chemical formula. The formula weight of an ionic compound is found by adding up all of the atomic weights of the atoms in the compound. The molecular weight is the formula weight of a molecule

Percent Composition of Compounds Mass percent is the ratio of the atomic weight of all the atoms of a certain element to the total formula of molecular weight of the substance.

Chemical Equations

Chemical reactions Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken Chemical reactions involve changes in matter, the making of new materials with new properties, or energy changes. Chemical Reactions are described using a shorthand called a chemical equation

Balancing equations Chemical equations show the conversion of reactants (the molecules traditionally shown on the left of the arrow) into products (the molecules traditionally shown on the right of the arrow). A + sign shows that the compounds on the left of the arrow combine to form the product or products on the right of the arrow. The arrow is read as “reacts to yield” Example C + O2  CO2 This reads carbon plus oxygen reacts to yield carbon dioxide

The charcoal used in a grill is basically carbon The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O2  CO2, contains the same information as the English sentence but has quantitative meaning as well.

Law of conservation of mass. An equation is balanced when the total number of atoms of each element occur the same number of times on both sides of the equation. Law of conservation of mass. Atoms are neither created nor destroyed in a chemical reaction. They may, however, be combined differently or converted into energy.

When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may not change the subscripts. Changing the subscripts changes the compound.

The meaning of subscripts and coefficients used with a chemical formula. The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

ACTIVITY 5 What is the law of conservation of mass? What is to balance chemical equation? What is chemical formula? What is chemical change? Can you evaluate the chemical change?

NAME 15 ELEMENTS YOU KNOW WHICH ARE METALS? WHICH ARE GASES? EXIT QUIZ NAME 15 ELEMENTS YOU KNOW WHICH ARE METALS? WHICH ARE GASES? WHICH ARE NOBLE GASES? WHICH ARE METALLOIDS?