Changes in Matter

The BIG Idea Everything around you is matter. All matter is made up of elements, the smallest unit of which is the atom, and is described by its properties and composition.

Objective 1 (CK) Atoms, Molecules, and Compounds Basics of atomic structure: nucleus, protons (positive charge), neutrons (neutral), electrons (negative charge) Atoms are constantly in motion; electrons move around the nucleus in paths called shells (or energy levels). Atoms may join together to form molecules and compounds. Common compounds and their formulas: Water: H20, “Table” salt: NaCl, Carbon dioxide: CO2

Objective 1 (CK) People have been thinking about matter for more than 2, 500 years. It was widely believed that all matter was composed of four elements – earth, air, fire, and water Read slide: Add: In the 5th century, the Greek philosopher Democritus hypothesized that matter was made of very small indivisible units. He used the Greek word atomos, meaning “invisible,” to describe a particle that could not be further subdivided.

The Atom In 1803, scientist and school teacher John Dalton came up with a precise definition for the invisible unit we call the atom today. Read Slide: Add: Dalton’s theory explained, among other things, that all elements are composed of extremely small particles called atoms; that all atoms of a given element are identical; and that the atoms of one element are different from atoms of any other.

The Atom We now know that atoms have an internal structure and area made of even smaller parts known as subatomic particles. These particles are protons, neutrons, and electrons. Read Slide: Add:

The Atom Protons are particles in the nucleus of an atom that have a positive (+) charge. Read Slide: Add:

The Atom Neutrons are uncharged (electrically neutral) particles that are also contained in the nucleus of an atom Read Slide: Add:

The Atom Electrons are negatively (-) charged particles that spin around the nucleus. Read Slide: Add: Although electrons are often compared to planets, the comparison is imperfect, because planets orbit the sun in very orderly and predictable paths, whereas it is difficult to pinpoint the exact path that electrons travel because they move so quickly. Electrons circle the nucleus, and form wheat is called an electron cloud.

The Atom Protons and electrons have exactly equal (but opposite) charges, so an atom tries to stay electrically “neutral” by having the same number of protons and electrons. Read Slide: Add: Protons and neutrons are in the nucleus of an atom and cannot be removed by ordinary chemical reactions, Electrons, however, are in shells around the nucleus, and can be added or removed during chemical reactions.

The Atom Read Slide: Add: Electrons are held around the nucleus by electrostatic forces. Although atoms can be divided into the part that make them up, once divided, they no longer represent an element or a complete unit of matter. The number of particles (protons and neutrons) in the nucleus and the number of electrons around the nucleus determine the properties of the element. An atom with one proton is an atom of the element hydrogen. An atom with two protons is an atom of helium. (Note that the number of electrons in any given atom is equal to its number of protons.)

Periodic Table Add: Look at this periodic table. The number above each symbol is called the atomic number. This number tells how many protons are in the nucleus of an atom of a particular element. You will see that no two elements have the same atomic number. There is only one kind of atom with 29 protons (copper), and only one kind with 30 (zinc). The atoms of a particular element are unique to that element.

The Atom Normally, an atom contains an equal number of electrons and protons, making the whole atom electrically neutral. This means that the negative charges of the electrons balance the positive charges of the protons in the atom.

The Atom If an atom loses any electrons , the atom become positively charged, and if it gains more electrons than protons, the atom becomes negatively charged. These positively and negatively charged atoms are called ions. Read Slide: Add: A positively charged atom will be attracted to a negatively charged atom, but repelled from another positively charged atom.

The Atom Like charges repel and unlike charges attract. When an object discharges, it loses the excess electrons and becomes neutral again. Read Slide: Add: For example: if you have ever combed your hair and had your hair stand up as a result, it was because your hair acquired electrons from the comb. The individual hairs, all being made of the same material, will each acquire the same charge and are repelled from each other, thus making them stand up or stick out. Since the comb has lost electrons, it has become positively charged and will be attracted to your negatively charged hair. Have you ever walked across a carpet and touched a doorknob, only to receive a shock and see a spark? When your feet rub against the carpet, electrons from the carpet are transferred to you, and this excess of electrons makes you become negatively charged. If you then touch another object, such as a metal doorknob, the electrons move from you to the doorknob, getting rid of the charge. This is called a discharge. Like charges repel and unlike charges attract.

The Molecule Two or more atoms that are chemically combined are called Molecules. Share one another’s electrons. A water molecule consists of two hydrogen atoms that are bonded to an atom of oxygen. Read Slide: Add:

Objective 2 (CK) Elements Elements have atoms of only one kind, having the same number of protons. There are a little more than 100 different elements. The periodic table organizes elements with common properties. Atomic symbol and atomic number Well known elements and their symbols

Objective 2 (CK) cont. Elements Two important categories of elements: metals and non-metals Metals compose about 2/3 of the known elements. Properties of metals: Most are shiny, ductile, malleable, conductive.

Elements Matter is composed of elements. Gold, silver, and aluminum, are all elements. They are pure substances that cannot be broken down into simpler substances. Read Slide: Add: Each of these elements has its own distinctive kind of atom: an atom of gold has 79 protons, and atom of silver has 47, an atom of aluminum has 13.

Periodic Table: Mendeleev In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table. He grouped elements according to their atomic mass, and as he did, he found that the families had similar chemical properties.  Blank spaces were left open to add the new elements he predicted would occur. 

Elements The Periodic Table arranges all elements according to their atomic number. atomic number = number of protons The table identifies elements with similar chemical properties.

Periodic Table Hand out Instructional Master 78a Add: Scientists have developed symbols of one to three letters, for the sake of convenience, to represent each of the elements. The first letter of the symbol is always capitalized and the remaining letters are not. Many of the symbols were derived from the first two letters of the either the Latin or the English name for the element. Gold, for example, was given the symbol Au from its Latin name, aurum. Nickel was given the symbol Ni from the first two letters of its English name.

Elements Some elements you may know: Oxygen – to breathe Helium – makes balloons float Calcium – helps make your bones strong Iron – to stay healthy and strong Read Slide: Add: These are examples of elements, the stuff that makes everything around us. Over 97% of the human body is composed of different combinations of just six elements –oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. In fact, most living things – trees, flowers, dogs, cats, fish, etc. – are largely made of these six elements.

Elements: Metals Read Slide: Add: Many elements are metals. Metals are good conductors of heat and electricity, and, with the exception of mercury (Hg), are solids at room temperature. Non metals are typically poor conductors of heat and electricity. Nonmetals may be solid (as in carbon, C), liquid (as in bromine, Br2), or gas (as in helium, He) at room temperature. Metalloids have properties between those of metals and nonmetals; for example, they may be good conductors of electricity, but may be brittle.

Properties of Metals Metals are good conductors of heat and electricity. Metals are shiny. Metals are ductile (can be stretched into thin wires). Metals are malleable (can be pounded into thin sheets). A chemical property of metal is its reaction with water which results in corrosion.

Common Elements and Symbols

Molecules A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. In the animation above, two nitrogen atoms (N + N = N2) make one Nitrogen molecule .

Substances: element or compound Elements- simplest kind of matter cannot be broken down any simpler and still have properties of that element! all one kind of atom. Compounds are substances that can be broken down only by chemical methods when broken down, the pieces have completely different properties than the original compound. made of two or more atoms, chemically combined (not just a physical blend!)

Compounds Atoms of two or more different elements bound together. Can be separated into elements chemically, but not physically. In the animation above, water (H20) is a compound made of Hydrogen and Oxygen. Animated images and notes from http://www.chem.purdue.edu/gchelp/atoms/elements.html

Lets Review Atoms Elements The building blocks of Matter Consists of Protons (+), Electrons (-), and Neutrons (N). Elements Consists of only one kind of atom, Cannot be broken down into a simpler type of matter by either physical or chemical means Can exist as either atoms or molecules. Images are from http://www.chem4kids.com

Chemical Bonds Molecules are groups of atoms held together in a stable association. Compounds are molecules containing more than one type of element. Atoms are held together in molecules or compounds by chemical bonds.

Objective 1 (CCSS) Describe that matter is neither created nor destroyed even though it may undergo change. Compare the total weight of an object to the weight of its individual parts after being disassembled. Compare the weight of a specified quantity of matter before and after it undergoes melting or freezing. Investigate the results of the combined weights of a liquid and a solid after the solid has been dissolved and then recovered from the liquid (e.g., salt dissolved in water then water evaporated). Investigate chemical reactions in which the total weight of the materials before and after reaction is the same (e.g., cream and vinegar before and after mixing, borax and glue mixed to make a new substance).

Compare the total weight of an object to the weight of its individual parts after being disassembled.

Objective 3 (CK, CCSS) Chemical and Physical Change Chemical change alters the composition of a molecule and results in a new substance with a new molecular structure. Examples of chemical change are the rusting of iron, the burning of wood, and milk turning sour.

Objective 3 (CK, CCSS) cont. Chemical and Physical Change Physical change alters only the properties or appearance of the substance, but does not change what the substance is made up of. Examples of physical change are cutting wood or paper, breaking glass, and freezing water.

Physical changes are those changes that do not result in the production of a new substance.  If you melt a block of ice, you still have H2O at the end of the change.   

If you break a bottle, you still have glass If you break a bottle, you still have glass.  Painting your nails will not stop them from being fingernails.  Some common examples of physical changes are: melting, freezing, condensing, breaking, crushing, cutting, and bending.

Some, but not all physical changes can be reversed Some, but not all physical changes can be reversed. You could refreeze the water into ice, but you cannot put your hair back together if you don’t like your haircut!

Special types of physical changes where any object changes state, such as when water freezes or evaporates.

Chemical changes, or chemical reactions are; changes that result in the production of another substance. 

FLAMMABILITY: A material’s ability to BURN in the presence of OXYGEN

REACTIVITY: How readily (easily) a substance combines chemically with other substances.

When you burn a log in a fireplace, you are carrying out a chemical reaction that releases carbon.  When you light your Bunsen burner in lab, you are carrying out a chemical reaction that produces water and carbon dioxide. 

Common examples of chemical changes that you may be somewhat familiar with are; digestion, respiration, photosynthesis, burning, and decomposition. 

Physical or Chemical Change? Burning Paper CHEMICAL

Physical or Chemical Change? Digestion of food CHEMICAL

Sugar dissolving in water PHYSICAL Physical or Chemical Change? Sugar dissolving in water PHYSICAL

Iron turning red when heated PHYSICAL Physical or Chemical Change? Iron turning red when heated PHYSICAL

Physical or Chemical Change? Evaporation PHYSICAL

A pond freezing in winter PHYSICAL Physical or Chemical Change? A pond freezing in winter PHYSICAL

Physical or Chemical Change? Melting ice PHYSICAL

Physical or Chemical Change? Cutting wire PHYSICAL

Physical or Chemical Change? Baking muffins CHEMICAL

Physical or Chemical Change? Shattering glass PHYSICAL

Decomposition of old leaves CHEMICAL Physical or Chemical Change? Decomposition of old leaves CHEMICAL