Elements. Explain what an element is and how many there are on the periodic table

Size: px

Start display at page:

Download "Elements. Explain what an element is and how many there are on the periodic table"

Elwin Wright
7 years ago
Views:

1 Elements Explain what an element is and how many there are on the periodic table

2 What are Atoms 2500 years ago people believed things were comprised of earth, air, fire and water BUT in 5th century bce, Greek Philosopher Democritus hypothesized that matter was made up of very small, invisible units he called them atomos to describe a particle that could no longer be subdivided Its was dismissed until 1803, where John Dalton came up with the precise definition we use today ATOM- the smallest unit of an element that still retains the properties of the element

3 Structure of an Atom after further study of the atom, we find that each atom contains more smaller parts known as subatomic particles called protons, neutrons and electrons Protons-a positively charged particle in the nucleus of an atom Neutrons- a neutral particle in the nucleus of an atom Electron- a negatively charged particle that spins around the nucleus of an atom

5 Atom Rules For an atom to be considered neutral, it needs to have the same amount of electrons and protons Protons and Neutrons CANNOT be removed by ordinary chemical reactions Electrons orbit (like the planets) around the nucleus and can be added or removed it is held around the nucleus by electrostatic forces (like gravity) Determining the properties of the element are based off the amount of protons, neutrons and electrons Example: 1 proton is Hydrogen 2 protons is Helium 79 protons is Gold

6 Atoms and Elements What we know about Atoms Atoms are the smallest units in life They have a set number of protons, neutrons and electrons example Gold: 79 protons, neutrons and electrons each. What is an Element? An element is a pure substance that cannot be broken down into simpler substances The element of oxygen is made up of only atoms of oxygen Some matter are made up of a combination of elements. example, Salt is a combination of sodium and chlorine

7 Periodic Table There are 115 elements on the Periodic Table 83 exist naturally on Earth 32 are made in laboratories by scientist Dimitri Mendeleev, a russian scientist, organized the periodic table that we use today He noticed a pattern in the way the elements combined with each other When they were arranged by atomic number (increasing heaviness), they were not only arranged by weight but by chemical activity called a period. hence the Periodic Table

8 Periodic Table The periodic table is divided into three groups: Metals, Nonmetals and Metalloids Many Elements are metals. With the exception of Mercury, they are all solids at room temperature Nonmetals examples solid like Carbon, liquid like iodine or gas like helium Metalloids are brittle Fun Fact!: 97% of the human body is composed of only 6 elements: oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus And fish, tres, flowers, cats and dogs!

9 Metals, Nonmetals, Metalloids Metals are great conductors of heat and electricity usually solid at room temperature (mercury is an exception) high luster (shiny), metallic appearance malleable (can be bent and pounded into thin sheets); ductile (can be drawn into wire) corrode or oxidize in air and sea water Nonmetals dull appearance usually brittle poor conductors of heat and electricity usually less dense, compared to metals usually low melting point of solids, compared with metals Metalloids show characteristics of metals and nonmetals. dull or shiny usually conduct heat and electricity, though not as well as metals often make good semiconductors often exist in several forms often ductile; often malleable

10 Combined Elements Elements can be combined to create compounds and mixtures When two elements are combined chemically they form a chemical compound. example would be hydrogen and oxygen chemically combine to water When two elements are combined physically they form a mixture the elements blend together without forming a new substance and the properties of elements remain unchanged Unlike compounds, mixtures can be easily separated back into the pure elements Most matter exists as a mixture of both elements or compounds examples brass, steel, most rocks and even your blood

11 Common Elements Hydrogen H A gas, the least dense element; bonds to oxygen to make water Helium He A low density gas; extremely unreactive in nature Carbon C A nonmetal; exists in nature as graphite, diamond and fullerenes (large carbon compounds that resemble soccer balls) the basis for organic compounds Nitrogen N A gas making up 78% of the air we breathe Oxygen O A gas making up 21% of the air we breathe; supports combustion Sodium Na A low density, soft, highly reactive metal; constitutes 50% of table salt Aluminium Al A common metal used in everyday items, good conductor of heat & electricity Silcon Si A metalloid, a constituent of sand used to make glass and computer chips Chlorine Cl A pale green, poisonous, highly reactive gas, constitutes 50% of table salt

12 Common Elements Iron Fe A strong, hard, magnetic metal; it is the major constituent of steel Copper Cu A metal; good conductor of heat and electricity. Often used to make wires and cookware Silver Ag A unreactive soft metal, often used in jewelry Gold Au A very unreactive yellow metal, often used in jewelry

13 Physical Changes Physical Change is when the physical properties of an element or compound change WITHOUT also changing the composition or identity of that element or compound When an element changes in size, state or is combined to form a mixture all falls under physical change Examples: breaking glass, cutting wood, mixing sugar with water. Water changing from ice, to liquid to gas all are physical changes

14 Chemical Changes Chemical Change: when two or more substances interact creating a new substance. A change occurs in the way atoms are linked or bonded. New properties then form that are different from the original substances. Example: when oxygen and hydrogen interact, they bond to make a new substance called water. Reactants: are the substances that change. Products: are the new substances Examples: rusting of iron, a birthday cake, souring of milk

15 How can We tell If a change results in an evolution of gas, the formation of light and heat or change in color, in most cases in a Chemical Change. Vinegar and baking soda is a chemical change with CO2 being omitted Wood burning emits light and heat Iron rusts the color changes Chemical Change is harder to undo that a Physical Change

Chapter Outline. 3 Elements and Compounds. Elements and Atoms. Elements. Elements. Elements 9/4/2013

Chapter Outline. 3 Elements and Compounds. Elements and Atoms. Elements. Elements. Elements 9/4/2013 3 Elements and Compounds Chapter Outline 3.1 Elements A. Distribution of Elements Foundations of College Chemistry, 14 th Ed. Morris Hein and Susan Arena Copyright This reclining Buddha in Thailand is