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Physical Science. Chapter 20: Chemical Bonds. Compounds. A compound is a combination of atoms from 2 or more different elements, in a definite ratio The properties of a compound may be completely different from those of the elements which make it up. Example: water (H 2 O).

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Physical science

Physical Science

Chapter 20: Chemical Bonds


Compounds
Compounds

  • A compound is a combination of atoms from 2 or more different elements, in a definite ratio

  • The properties of a compound may be completely different from those of the elements which make it up.

  • Example: water (H2O)


Chemical formulas
Chemical Formulas

  • A short-hand way to write the name of a chemical compound is by using a chemical formula, which is like a "recipe" for a compound.

  • It tells what elements are in the compound, and how many atoms of each element.



  • Molecule - smallest sample of a compound.

  • Molecular mass - the mass of a single molecule of a compound.

  • Ex. H2O (2x1) + (1x16) = 18



  • C water?6H12O6 is the chemical formula for a simple sugar. What is the molecular mass of this compound?


Chemical stability
Chemical stability water?

  • Some elements do not join together with other elements to form compounds. These un-reactive elements are said to already be chemically stable.

  • All of the elements in G18 are this way.


  • The way that an element reacts with other elements is determined by it's outer shell electrons.

    (Outer shell electrons refers to the electrons that are farthest out from the nucleus in the electron cloud)

  • Atoms which react with each other do so by either gaining, losing, or sharing electrons with other atoms.



  • Likewise, atoms of different elements can only have a certain # of electrons in their electron clouds, and if they are full then they are stable, and won’t react with other elements.

  • Elements with 8 o.s.e.’s, or a full first level (2 e-’s) are stable, and will not react.



  • An may react with certain other elements.electron dot diagram can show how many outer shell electrons an atom has, and whether or not it can hold any more, and therefore whether that atom will react or not.


Electron dot diagrams
Electron Dot Diagrams may react with certain other elements.

  • (Note: The only elements we will concern ourselves with now are the G1 & G2 metals, and the non-metals, since these are the most common reactive elements)

  • An element with 8 electrons in the outer shell is considered full, and stable (un-reactive). This is called the Octet Rule.

    Ex. He-2 ose's, Ne-8, Ar-8, Kr-8




  • Examples: for each outer shell electron up to 8.

    H He Al C

    N O Cl Ne



Chemical bonds
Chemical Bonds and un-reactive.

  • When 2 atoms do react with each other to form a new substance, this new substance is held together with chemical bonds. A chemical bond is a force holding the atoms in a compound together.

  • Think of bonds like the connecting sticks in a Tinkertoy set.


Types of bonds
Types of Bonds and un-reactive.

  • There are 2 main types of chemical bonds:

    1. Ionic - bonds created by the attraction of opposite charges (+, -) like a magnet

    2. Covalent - bonds created by the sharing of electrons


Ionic bonds
Ionic Bonds and un-reactive.

  • When 2 atoms react with each other, they both want to have a stable relationship (i.e. have 8 outer shell electrons)

  • Sometimes, one atom will "steal" electrons from another atom in order to become stable.


  • For example, sodium (Na) has 1 outer shell electron and chlorine (Cl) has 7.

    If chlorine were to gain 1 electron, then it would have 8, and be stable.

    So it "steals" sodium's electron to become

    stable.

    Sodium, however, now drops down an energy level and ends up with 8 outer shell electrons also. So everybody's happy.


  • When 1 atoms steals (gains) electrons, it will take on a negative charge since that is the charge of the electrons.

  • Likewise, the atom which gave up electrons will take on a positive charge, since it lost negatively charged electrons.

  • So………the 2 atoms now have opposite charges which attract each other, just like a magnet.


  • When the atoms join together, the positive and negative charges will cancel each other out, forming a neutral molecule.

  • Ions are individual atoms with a positive or negative charge due to gained or lost electrons

  • Ionic bonds form when the oppositely charged ions attract each other


Covalent bonds
Covalent Bonds charges will cancel each other out, forming a neutral molecule.

  • A covalent bond is formed when atoms combine together by sharing electrons.

  • Covalent bonds usually occur between 2 non-metals

  • Example: H has 1 o.s.e. and Cl has 7.

    By sharing, H will have 2 (stable)

    and Cl will have 8 (stable)


  • A charges will cancel each other out, forming a neutral molecule.diatomic molecule is one with 2 atoms of the same element covalently bonded.

  • Ex.: Cl2 (chlorine gas)

    O2 (oxygen gas)


Binary compounds
Binary Compounds charges will cancel each other out, forming a neutral molecule.

  • A binary compound is one composed of atoms from exactly 2 different elements.

  • In order to determine the ratio between 2 elements which will produce a compound it is often useful to use oxidation numbers

    (numbers which show how many electrons are gained, lost, or shared when 1 atom combines with another).


Using oxidation numbers to determine chemical formulas
Using oxidation numbers to determine chemical formulas. charges will cancel each other out, forming a neutral molecule.

Oxidation numbers show the number of electrons gained, lost, or shared when an atom combines.

Oxidation numbers are the same for elements in the same groups.*

Ex.: G17 elements gain 1 electron when bonding, and thus have an ox. # of -1.


+1 +2 +3 +4 -3 -2 -1 0


The criss-cross method +3 +4 -3 -2 -1 0

Oxidation numbers can be written as a superscript for each of the elements in a binary compound. Those numbers are then criss-crossed down and used as subscripts for the other element.

  • Example:

    Mg+2 N-3

    Cross the +2 and the -3 down to the subscript of the other element, drop the signs, and you end up with Mg3N2.


  • Example #2: +3 +4 -3 -2 -1 0

    Calcium has an oxidation # of +2, chlorine is -1, what is the formula for a compound of calcium and chlorine?


Naming binary compounds
Naming Binary Compounds +3 +4 -3 -2 -1 0

  • To name a binary compound, you simply say the name of the first element, and then add the suffix -ide to the root of the second element.

  • Example: Na + Cl = sodium chloride

    Al + N = aluminum nitride

    Ca + P = calcium phosphide


Toxic and corrosive materials
Toxic and Corrosive Materials +3 +4 -3 -2 -1 0

  • Many compounds are completely harmless to humans, while some are very harmful.

  • Corrosive materials attack and/or destroy metals, living tissue, and other materials.

    Acids are corrosive, although their relative strength will vary greatly.


  • Toxic +3 +4 -3 -2 -1 0 materials are poisonous.

  • If toxic materials are ingested, vomiting is often induced to remove the materials from the body.

    This is usually not the case with corrosive materials. Why?


Sample problems
Sample Problems +3 +4 -3 -2 -1 0

Write formulas, give names, and calculate molecular masses for each of the following compounds:

Al + Cl

Ca + O

Na + N

H + S

K + F



  • Identify 2 specific materials for each of the following: listed in order from most stable to least stable. What do you think is the main determining factor of stability in these molecules?

    A. Corrosive

    B. Toxic

    C. Corrosive, but not toxic

    D. Toxic, but not corrosive

    (assume materials are at everyday common strengths)


+1 +2 +3 +4 -3 -2 -1 0 listed in order from most stable to least stable. What do you think is the main determining factor of stability in these molecules?


  • Identify the following: listed in order from most stable to least stable. What do you think is the main determining factor of stability in these molecules?

    -P3 element with 6 outer shell electrons

    -the lightest inert element

    -the lightest binary compound (17 a.m.u.)

    -the lightest diatomic molecule



Give 1 example for each of the following: composed of hydrogen and sulfur:

  • A diatomic molecule which is very stable

  • A compound formula which reduces down to a 1:1 ratio

  • An element which loses 2 electrons when ionically bonding

  • An element which does not follow the Octet Rule


Physical science1

Physical Science composed of hydrogen and sulfur:

Ch. 21: Chemical Reactions


  • A composed of hydrogen and sulfur:chemical reaction is where 1 or more substances are chemically changed into new substance(s)

  • Example: Changing hydrogen gas and oxygen gas into water



Chemical equations
Chemical Equations both reactants and products.

A short-hand way to show a chemical reaction by using formulas and symbols is called a chemical equation.

Example: H2 + O2g H20

In a chemical equation, the reactant(s) are always on the left hand side, and the product(s) are always on the right.





Law of conservation of mass
Law of Conservation of Mass you will need to be familiar with.

  • In a chemical reaction, mass can neither be created or destroyed, it can only change form.

    Therefore, the mass of the reactants before the reaction occurs must be exactly equal to the mass of the products following the reaction.



Molecular mass
Molecular Mass set on fire. The products (smoke, ash, gases, etc.) would have the exact same mass as the log before it were burnt.

  • Molecular mass is the mass of 1 molecule of a given compound.

    Example: Calcium Chloride (CaCl2)

    Calcium atomic mass = 40 a.m.u.

    Chlorine atomic mass = 35 a.m.u. (x2)

    40 + (35 x 2 atoms) = 110 a.m.u.



  • For example, some household cleaners like Windex contain ammonia (NH4), a strong base.

  • Others, like Liquid Plumber, contain sulfuric acid (H2SO4). Mixing these can produce a violent reaction.

  • Or even worse, mixing ammonia with bleach can result in the production of poisonous chlorine gas (Cl2).


Types of reactions
Types of Reactions ammonia (NH

  • A synthesis reaction is one where 2 or more reactants will combine to produce 1 product.

    A + B g AB

    A decomposition reaction is where 1 reactant will break down into 2 or more products.

    AB g A + B


Thermal reactions
Thermal Reactions ammonia (NH

  • An exothermic reaction is one where energy (heat, light, or electricity) is given off during the reaction.

    Example: burning, pocket hand warmers, glowsticks, batteries, electric eels


  • In an ammonia (NHendothermic reaction, heat is taken in during the reaction. This causes the surrounding area to be cooled.

    Example: chemical cold pack


Catalysts
Catalysts ammonia (NH

  • A catalyst is a substance which will speed up the rate of a chemical reaction, without changing the product(s).

  • Ex: blowing on a fire, moisture speeding up the rate of corrosion, heating Luminol


Inhibitor
Inhibitor ammonia (NH

  • An inhibitor is a substance which slows down a chemical reaction without changing the product(s).

    Ex: lemon juice on an apple, food preservatives, CO2

    on a fire, cooling Luminol




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