Crash course on symbols and equations

Lesson outcome Describe the structure of atoms. Describe what ions are. Be able to work out the charges on the ion. Write formulas for compounds. Write equations and balance them.

What are atoms? What is proton/neutron/electron? What does atomic number indicate? What does mass number show?

What are atoms? atomic number = number of protons, also the number of electrons. Mass number = number of protons plus the number of neutrons.

Electron configuration of atoms Electrons of atoms are arranged in energy shells, the first shell can accommodate 2 electrons, 8 for the second shell and 8 for the third shell. The shells are stable if it is full of electrons.

Ions Ions are atoms that have gained or lost electrons from other atoms in order to be stable, which means it has a different number of electron compared to its proton.

Ions Ions are atoms that have gained or lost electrons from other atoms in order to be stable, which means it has a different number of electron compared to its proton.

The charges on the ion Depending on how many electrons an atom has lost or gained, the charge on the ion can be +/- 1, 2 ,3. If an atom has lost electron it will be a positive ion. If an atom has gained electron it will be a negative ion.

The charges on the ion Magnesium loses 2 electrons to become Mg2+ If an atom has lost or gained two or more electrons their charge will be higher respectively. e.g. Magnesium loses 2 electrons to become Mg2+ Oxygen gains 2 electrons to become O2-.

Ionic compounds Mg2+ is attracted to O2- to form MgO. Positive and negative ions are attracted to each other by electrostatic attraction. e.g. Mg2+ is attracted to O2- to form MgO. When we write the symbol for the compound we don’t include the charge as they are neutral. We call compounds cation first and anion last. e.g. MgO is magnesium oxide.

Ionic formulas What’s the electron configuration for calcium? What’s the difference between atoms and ions? What’s the electron configuration for calcium ion? What’s the charge on oxide ion? What’s the formula for the compound Cu2+ and OH-?

Common mistakes

Balancing Equations

Vocabulary Coefficient: is a small, whole number that appears IN FRONT of a chemical formula in a chemical equation. Example: 4 HCl Word Equation: an equation in which the reactants and products in a chemical reaction are represented by words. Example: hydrogen + oxygen yields water Formula Equation: represents the reactants and products of a chemical reaction by their symbols or formulas. Example: 2 H2 + O2  2 H2O

Write and balancing equations Write word equation. Write symbol equation by replacing words with symbols. Count the number of atoms on the left hand side. Count the number of atoms on the right hand side. Change the coefficient to make the number of atoms of each element equal on both side of the arrow. Write the balanced symbol equation in full. Check your work.

__Fe2O3 + __H2SO4  __Fe2(SO4)3 + __H2O Examples: __Al + __O2  __Al2O2 __C2H6 + __O2  __CO2 + __H2O __Fe2O3 + __H2SO4  __Fe2(SO4)3 + __H2O

Make a question On a piece of paper: Either 1. Pick an equation from the sheet Or 2. Write an equation yourself. The problem will be solve by whoever that picks up your questions next class. Have fun : )

Why are we learning this? The coefficients of a chemical reaction indicate relative amounts of reactants and products. Coefficients are MOLE RATIOS Example: H2(g) + Cl2(g)  2HCl(g) 1 mol H2 : 1 mol Cl2 : 2 moles HCl The relative masses of the reactants and products can also be determined from the coefficients. Example: 1 mol H2 = 2.02 g H2 1 mol Cl2 = 70.90 g Cl2 2 mol HCl = 72.92 g HCl

Law of Conservation of Mass The law of conservation of mass states that matter is neither lost nor gained in chemical reactions. It simply changes form.

Dalton’s Law of Definite Proportions Atoms are indestructible and unchangeable, so compounds are formed when one atom chemically combines with other atoms. When elements react to form compounds, they react in defined, whole-number ratios. Reactions are not random events. They proceed according to precise and well-defined formulas.