Chemistry Learning Targets  Describe the relative charges, masses, and locations of the protons, neutrons, and electrons in an atom of an element.  Explain the arrangement of the elements on the Periodic Table, including the relationships among elements in a given column or row.  Describe the role of valence electrons in the formation of chemical bonds.  Describe the relative charges, masses, and locations of the protons, neutrons, and electrons in an atom of an element.  Explain the arrangement of the elements on the Periodic Table, including the relationships among elements in a given column or row.  Describe the role of valence electrons in the formation of chemical bonds.  Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.  Describe a chemical reaction using words and symbolic equations.  For example: The reaction of hydrogen gas with oxygen gas can be written: 2H 2 + O 2 → 2H2O.  Relate exothermic and endothermic chemical reactions to temperature and energy changes.

Matter  Matter is anything that has a mass and volume  Matter is composed of elements  Elements are substances that cannot be broken down by ordinary chemical means Each element is made of 1 type of atom  Matter is anything that has a mass and volume  Matter is composed of elements  Elements are substances that cannot be broken down by ordinary chemical means Each element is made of 1 type of atom

What is matter made of? Atoms are the building blocks of matter The smallest part of an element that has all the properties of the element Atoms are the building blocks of matter The smallest part of an element that has all the properties of the element

Structure of an atom Nucleus (center) contains protons and neutrons Each protons has a +1 charge Each neutron has 0 (neutral) charge Nucleus (center) contains protons and neutrons Each protons has a +1 charge Each neutron has 0 (neutral) charge

Electrons are in energy levels orbiting around the nucleus Each electron has a -1 charge The row number of an element in the periodic table indicates how many energy levels it has. Electrons pair up and fill in with 2 in the first level, then 8 in the next, etc. Each electron has a -1 charge The row number of an element in the periodic table indicates how many energy levels it has. Electrons pair up and fill in with 2 in the first level, then 8 in the next, etc.

What do the outer electrons mean?  The number lets us work out how they react.  Referring to the number of electrons in the outside of the atom with 0 actually meaning 8.  The goal of all atoms is to have a full outer ring (usually 8 electrons). To do this they must either react to gain or lose electrons.  The number lets us work out how they react.  Referring to the number of electrons in the outside of the atom with 0 actually meaning 8.  The goal of all atoms is to have a full outer ring (usually 8 electrons). To do this they must either react to gain or lose electrons.

Atoms vs. Ions vs. isotopes Atoms have the same number of protons as electrons and are neutral (no charge) Ions have a different charge. Ions have gained or lost electrons (have a positive or negative charge) Atoms have the same number of protons as electrons and are neutral (no charge) Ions have a different charge. Ions have gained or lost electrons (have a positive or negative charge)

Isotopes have a different mass because they have more or less neutrons. Hydrogen has 1 proton, 1 electron and 0 neutrons Deuterium has 1 protons, 1 electron and 1 neutron -Tritium has 1 proton, 1 electron and 2 neutrons

Isotopes Models of two isotopes of boron are shown. Because the numbers of neutrons in the isotopes are different, the mass numbers are also different. You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11.

Identifying Isotopes The average atomic mass of an element is the weighted-average mass of the mixture of its isotopes. For example, four out of five atoms of boron are boron-11, and one out of five is boron-10. To find the weighted-average or the average atomic mass of boron, you would solve the following equation:

Using the periodic table The Atomic Number is equal to the number of protons in the nucleus. In neutral atoms this is also equal to the number of electrons The Atomic Mass is the average mass of all the elements isotopes. The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom. The Atomic Number is equal to the number of protons in the nucleus. In neutral atoms this is also equal to the number of electrons The Atomic Mass is the average mass of all the elements isotopes. The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom.

What about Neutrons?  If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons.  This is specific for each isotope of that element.  number of neutrons = mass number – atomic number  If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons.  This is specific for each isotope of that element.  number of neutrons = mass number – atomic number

Periodic Table of Elements Using colored pencils or crayons create a key for your periodic table.

Arrangement of elements on the periodic table  Rows of elements are called periods  Atomic number increase across a period  Columns of elements are called groups  Elements have similar chemical properties  Rows of elements are called periods  Atomic number increase across a period  Columns of elements are called groups  Elements have similar chemical properties

On your chart fill in the numbers corresponding with the Groups. These numbers correlate with the amount of electrons contained in the element.

Metals: Most elements are metals! High Shine good conductor malleable (easy to shape) Easily lose electrons (positive charge)

Non-metals: Low Shine / Dull Poor Conductor Brittle (breakable) Tend to gain electrons (negative charge)

Periodic Table of Elements

Metalloids Have properties of both metals & nonmetals shiny or dull solids can conduct some heat, not as well as metals

Ionic Bond Because non metals gain electrons and metals lose electrons the atoms are attracted to each other. (+ and - attract) Between metals and non metals example: sodium (Na) + chlorine (Cl) = NaCl

Gain or Loss of Electrons Some of the most common compounds are made by the loss and gain of just one electron. Some examples are sodium chloride, commonly known as table salt; sodium fluoride, an anticavity ingredient in some toothpastes; and potassium iodide, an ingredient in iodized salt.

A Bond Forms A neutral atom of potassium has one electron in its outer level. This is not a stable outer energy level. When potassium forms a compound with iodine, potassium loses one electron from its fourth level, and the third level becomes a complete outer level.

A Bond Forms The potassium atom has become an ion. When a potassium atom loses an electron, the atom becomes positively charged because there is one electron less in the atom than there are protons in the nucleus The 1+ charge is shown as a superscript written after the element’s symbol, K +, to indicate its charge.

A Bond Forms The iodine atom in this reaction undergoes a change. An iodine atom has seven electrons in its outer energy level. During the reaction with potassium, the iodide atom gains an electron, leaving its outer energy level with eight electrons.

A Bond Forms This atom is no longer neutral because it gained an extra negative particle. It now has a charge of 1− and is called an iodide ion, written as I −.

A Bond Forms Notice that the resulting compound has a neutral charge because the positive and negative charges of the ions cancel each other.

The Ionic Bond The formation of magnesium chloride, MgCl 2, is another example of ionic bonding. When magnesium reacts with chlorine, a magnesium atom loses two electrons and becomes a positively charged ion, Mg 2+.

The Ionic Bond At the same time, two chlorine atoms gain one electron each and become negatively charged chloride ions, Cl −.

Covalent bonds Formed between 2 nonmetals sharing 2 or more electrons Example: Water molecule is formed when 2 Hydrogen atoms share electrons with one Oxygen atom.

Sharing Electrons Some atoms of nonmetals are unlikely to lose or gain electrons. For example, the elements in Group 4 of the periodic table have four electrons in their outer levels. They would have to either gain or lose four electrons in order to have a stable outer level.

Sharing Electrons The loss of this many electrons takes a great deal of energy. Therefore, these atoms become more chemically stable by sharing electrons, rather than by losing or gaining electrons. Click image to view movie

Sharing Electrons The attraction that forms between atoms when they share electrons is known as a covalent bond. A neutral particle that forms as a result of electron sharing is called a molecule.

Unequal Sharing Electrons are not always shared equally between atoms in a covalent bond. These elements are close together in the upper right- hand corner of the periodic table. The strength of the attraction of each atom to its electrons is related to the size of the atom, the charge of the nucleus, and the total number of electrons the atom contains.

Unequal Sharing Part of the strength of attraction has to do with how far away from the nucleus the electron being shared is. The other part of the strength of attraction has to do with the size of the positive charge in the nucleus.

Unequal Sharing Chlorine atoms have a stronger attraction for electrons than hydrogen atoms do. One example of this unequal sharing is found in a molecule of hydrogen chloride, HCl. Click image to view movie

Unequal Sharing As a result, the electrons shared in hydrogen chloride will spend more time near the chlorine atom than near the hydrogen atom.

Polar or Nonpolar? A polar molecule is one that has a slightly positive end and a slightly negative end although the overall molecule is neutral. Water is an example of a polar molecule. The charge is balanced but not equally distributed. This type of molecule is called polar bond.

Polar or Nonpolar? Such a molecule does not have oppositely charged ends. A nonpolar molecule is one in which electrons are shared equally in bonds. This is true of molecules made from two identical atoms or molecules that are symmetric, such as CCl 4.

Energy  The primary source of energy for the Earth is the sun  Energy cannot be created or destroyed in ordinary reactions, only changed from one form to another. (First Law of Thermodynamics)  Exceptions to this law are nuclear reactions, fission and fusion  Nuclear reactions do create large amounts of energy from small amounts of matter  Example - solar power is created through the fusion (combining) of 4 hydrogen atoms into 1 helium atom  The primary source of energy for the Earth is the sun  Energy cannot be created or destroyed in ordinary reactions, only changed from one form to another. (First Law of Thermodynamics)  Exceptions to this law are nuclear reactions, fission and fusion  Nuclear reactions do create large amounts of energy from small amounts of matter  Example - solar power is created through the fusion (combining) of 4 hydrogen atoms into 1 helium atom

Examples of the energy changing forms  Food chains are examples of energy changing form  Solar energy is trapped by pigments in plants  This is converted to chemical energy stored in the bonds of sugars  Animals that eat the plants obtain chemical energy  Chemical energy stored in gasoline is released in your car through combustion  This turns to mechanical energy to allow your car to move  Another way to state this law is  You can’t make something from nothing  We cannot create energy  Food chains are examples of energy changing form  Solar energy is trapped by pigments in plants  This is converted to chemical energy stored in the bonds of sugars  Animals that eat the plants obtain chemical energy  Chemical energy stored in gasoline is released in your car through combustion  This turns to mechanical energy to allow your car to move  Another way to state this law is  You can’t make something from nothing  We cannot create energy

Energy changing form

Second Law of Thermodynamics  When energy changes form, it becomes less and less useful.  Most of it is lost as heat  In other words, you can’t make something from nothing…  You can’t even break even  When energy changes form, it becomes less and less useful.  Most of it is lost as heat  In other words, you can’t make something from nothing…  You can’t even break even

The Law of Conservation of Mass  Matter cannot be created or destroyed by ordinary chemical means  In any chemical reaction, the amount of reactants must = amount of products  Photosynthesis  6 CO H 2 O + Light energy → C 6 H 12 O O 2  Matter cannot be created or destroyed by ordinary chemical means  In any chemical reaction, the amount of reactants must = amount of products  Photosynthesis  6 CO H 2 O + Light energy → C 6 H 12 O O 2

The Fun World of Chemical Reactions!  What goes in, must come out. But what do we call the stuff that is going in/out?  Reactants – starting material in a chemical reaction  Products – a substance that is formed as a result of a chemical reaction  What goes in, must come out. But what do we call the stuff that is going in/out?  Reactants – starting material in a chemical reaction  Products – a substance that is formed as a result of a chemical reaction

Oh How we Love Table Salt  Example:  Sodium (Na) + Chlorine (Cl) = NaCl (table salt)  In this reaction what are the reactants and what is the product?  Example:  Sodium (Na) + Chlorine (Cl) = NaCl (table salt)  In this reaction what are the reactants and what is the product?

Indicators of chemical change -Creation of gas – bubbles - change in color -Precipitate – new solid substance - change in odor - change in temperature: -Increase -decrease

Energy in a reaction Endothermic reactions take in energy from the environment Example – ice melting Exothermic reactions release energy into the environment Example – combustion, bombs exploding Endothermic reactions take in energy from the environment Example – ice melting Exothermic reactions release energy into the environment Example – combustion, bombs exploding