BC Science 10 Chapter 4

Strategies for Balancing Equations

- Use trial and error. If you are not sure where to place the first coefficient, just start anywhere. For simple equations, this is often the fastest method.- Balance compounds first and single elements last. - Finish balancing all atoms in one formula after you have placed a coefficient in front. Do not jump from one pure substance to another before balancing the first formula. - Add coefficients only in front of formulas. Do not change subscripts. - Sometimes, oxygen or hydrogen will appear in more than one place on the reactants side or on the products side of the chemical equation. This is your signal to balance oxygen and hydrogen last. Once you have finished balancing the other elements, you may find that the oxygen and hydrogen are already balanced. - Perform a final check once you are finished to be sure that all elements are balanced.

Bohr Diagram

-A diagram that shows how many electrons are in each shell surrounding the nucleus. -Each atomic shell can hold a certain amount of electrons

Diatomic Molecule

-A pair of atoms that are joined by covalent bonds. -Only 7 diatomic molecules

Poly-atomic Ion

-An ion composed of more than one type of atom joined by covalent bonds. -They carry a charge and therefore cannot exist on their own

Multivalent Metals

-Can form two or more different positive ion charges -Nickel (Ni) has two charges of 2+ and 3+ -To distinguish between two ions formed from multivalent metals, you need to name each ion and it must contain the charge of the ions using roman numerals -Nickel (II) represents nickel "2+"

Naming Ionic Compounds

-Cation - Metal atoms that is positively charged -Anion - Non-Metal atoms that are negatively charged

Ionic Compounds

-Contains a positive ion (usually a metal) and a negative ion (usually a non-metal) -One or more electrons transfer from each atom of the metal to each atom of the non-metal.

Periodic Table

-Each element is listed according to its atomic number -Rows are called periods -Each column (up and down) is called a group/family -Metals are on the left and middle -Non-metals are in the upper right corner -Metalloids form a staircase on the right side -Elements in the same family have similar properties (alkali metals, alkaline earth metals, halogens, noble gas) -Alkali metals (very reactive) -Alkaline earth metals (somewhat reactive metals) -Halogens (very reactive non-metals) -Noble gasses (very unreactive gaseous non-metals) -Transition metals, groups 3 through 10 -Period number represents that amount of shells that are occupied.

Valence Electrons

-Electrons that are found in the valence shell -Electrons involved in chemical bonding -Groups correspond with the number of electrons in the shell

Lewis Diagram of Compounds and Ions

-For positive ions, one electron dot is removed from the valence shell for each positive charge of the ion. This usually means all the electron dots are removed. Only the element symbol remains encased in square brackets with a positive charge shown at the top right. - For negative ions, one electron dot is added to each valence shell for each negative charge of the ion. This usually means the element's symbol is surrounded by eight electron dots (two electron dots for hydrogen). Square brackets are placed around the diagram with a negative charge shown at the top right

Covalent Compounds

-H,2 0,2 is known as hydrogen peroxide -It doesn't not get changed to HO because the subscripts in Covalent Compounds mean different things than Ionic Compounds -In an ionic compound, subscripts are used to show the smallest whole-number ratio of the ions. -In a covalent compound, the subscripts show the actual number of atoms of each element in the molecule.

If the Compound is Ionic

-If the positive ion is a metal, the periodic table will show whether it has one or more than one ion charge. - For a metal with only one form of ion, the ion simply takes the name of the element. For example, the name of Ba2 is the barium ion. - For a metal with more than one form of ion (multivalent), a Roman numeral is added to the name of the first element (the metal). The Roman numeral indicates the ion's charge. For example, nickel has two common ion charges, so the name of Ni2 is nickel(II), and the name of Ni3 is nickel(III). • If the negative ion comes from a single non-metal atom (such as P3) then the name of the ion ends with the suffix "-ide." For example, K3P is called potassium phosphide, and Fe2O3 is called iron(III) oxide. • If the negative ion is a polyatomic ion, look up the formula. Use that name in the compound's name. Pay close attention to the endings (suffixes). Some examples include the following. (NH4)2S is ammonium sulfide (NH4)2SO4 is ammonium sulfate Na2SO4 is sodium sulfate Na2SO3 is sodium sulfite

Ionic Compounds vs Covalent Compounds

-Ionic compounds begin with a metal or the ammonium ion - If the formula starts with a non-metal, it is likely that it is a covalent compound. There are special rules for compounds with hydrogen.

Coefficients

-Numbers placed in front of a chemical formula or a chemical symbol for an element that show the ratios between the various compounds in a chemical reaction 2NO(g) O2(g) ➔ 2NO2(g) For example, in the reaction above, the coefficients show that two molecules of NO react with one molecule of O2 to form two molecules of NO2. In other words, NO and O2 react in a 2:1 ratio.

Chemical Changes

-One or more chemical changes that occur at the same time -Involves the conversion of pure substances (elements and compounds) called reactants into other pure substances called products with different properties from the reactants.

The law of the conservation of mass

-States that mass is conserved in a chemical reaction; the total mass of the products is always equal to the total mass of the reactants in a chemical reaction -The idea that atoms are conserved (neither made nor destroyed) is believed to be true for all chemical reactions

Protons

-Subatomic particles that have a +1 (positive) electric charge. -Exist in the nucleus

Covalent Compounds

-The atoms of many non-metals share electrons with other non-metal atoms -formed when non-metallic atoms share electrons to form covalent bonds.

Subscript

-The small number written to the right of the symbol of an element -A subscript gives the ratio of each type of ion in the compound

Atom

-The smallest particle of any element that retains the properties of the element -50million atoms lined up would be about 1cm long -All neutral atoms of the same element have equal protons and neutrons

Ion

-When an atom gains or loses electrons, they become electrically charged particles called ions. - Metal atoms lose electrons to form positively charged ions called cations -Non-metals gain electrons and form negatively charged ions anions A - Atomic Number B - Ion Charge C - Symbol D - Name E - Atomic Weight

Forming Compounds

-When two atoms get close their valence electrons interact and a chemical bond forms if the new arrangement of atoms is stable -Stability of an atom is related to its energy -Atoms of metals may lose electrons -Atoms of non-metals may gain electrons from other atoms

Writing Formulas of Ionic Compounds

1. Identify each ion and its charge 2. Determine the total charges needed to balance positive with negative 3. Note the ratio of positive ions to negative ions 4.Use subscripts to write the formula.

Writing the Formula of a Compound Containing Poly-Atomic Ions

1. Identify each ion and its charge. 2.Determine the total charges needed to balance positive with negative 3.Note the ratio of positive ions to negative ions 4. Use brackets around ions to correctly show the ratio of ions 5. Use subscripts and brackets to write the formula. Omit brackets if only one ion is needed

Naming Ionic Compounds Containing Multivalent Metals

1. Identify the metal. 2. Verify that it can form more than one kind of ion by checking the periodic table. 3. Determine the ratio of the ions in the formula. 4. Note the charge of the negative ion from the periodic table. 5. The positive and negative charges must balance out. Determine what the charge needs to be on the metal ion to balance negative ion 6. Write the name of the compound.

Writing Names of Binary Covalent Compounds

1. Name the left most element in the formula 2.Name the second element, making sure the element name end with the suffix "ide" 3.Add prefix to the elements name to indicate the number of atoms of each element in the compound Exceptions: -If the element has only one atom, do not add a prefix -The prefix "mono" is shortened to "mon-" if it is placed before oxide

Lewis Diagram

A diagram that illustrates chemical bonding by showing only an atom's valence electrons and the chemical symbol.

Covalent Molecule

A group of atoms in which the atoms are bound together by sharing one or more pairs of electrons.

Lone Pair

A pair of electrons in the valence shell that is not used in bonding

Element

A pure substance that cannot be broken down into simpler substances

Compound

A pure substance that is composed of two or more atoms combined in a specific way.

Symbolic Equation

A set of chemical symbols and formulas that identify the reactants and products in a chemical reaction 2NO(g) O2(g) ➔ 2NO2(g)

Balancing Chemical Equations

CO2 H2O ➔ C6H12O6 O2 becomes 6CO2 6H2O ➔ C6H12O6 6O2

Chemical Changes

Changes the way the atoms and molecules, in a pure substance, are arranged and interconnected.

Ionic Compounds

Compounds that are composed of positive ions and negative ions.

Binary Covalent Compound

Contains two non-metal elements joined together by one or more covalent bonds.

If the Compound is Covalent

If the covalent compound is binary (and does not begin with hydrogen), then use the prefix naming system. For example, P2F4 is binary because it has only two elements, and it is covalent because it begins with a non-metal. Using the prefix naming system, its name is diphosphorus tetrafluoride.

Subatomic Particles

Individual atoms are composed of three subatomic particles, which are called protons, neutrons, and electrons

State of Matter

Letters indicate the compound's state: (g) for gas; () for liquid; (s) for solid; (aq) for aqueous (dissolved in water).

Multivalent

Metals that can form ions in more than one way, depending on the chemical reaction they undergo

Products

Pure substances formed in a chemical change that have different properties from those of the reactants

Reactants

Pure substances that react in a chemical change

Skeleton Equation

Shows the formulas of the reactants and products. K O2 ➔ K2O

Balanced Chemical Equation

Shows the identities of each pure substance involved as well as the matching number of atoms of each element on both sides of a chemical equation 4K O2 ➔ 2K(2)O

Neutrons

Subatomic particles that do not have an electric charge -Exist in the nucleus

Electrons

Subatomic particles that have a -1 (negative) electric charge. -Exist in the shells/energy levels around the nucleus

Stable Octet

The arrangement of eight electrons in the outermost shell

Valence Shell

The outermost shell that contains electrons

Bonding Pair

The pair of electrons involved in a covalent bond

Chemical Equation

The representation of a chemical reaction in words or symbols nitrogen monoxide oxygen ➔ nitrogen dioxide

Atomic Number/Nuclear Charge

The term given to the electric charge on the nucleus, and it is simply found by counting the number of protons. Atomic Number = # of protons = # of electrons

Balancing Equation Examples

Un-balanced - ___ C2H6 ___ O2 ➔ ___ CO2 ___ H2O Balanced - 2C2H6 7O2 ➔ 4CO2 6H2O