Chapter 1 Elements , Compounds, and Mixtures

1. Chapter 1Elements, Compounds, and Mixtures

2. What is matter made of? • About 450 B.C. a Greek philosopher named Empedocles proposed that all matter was made of 4 “elements” – air, earth, fire, and water • He thought all matter was a combination of two or more of these 4 elements • People believed this for more than 2,000 years

3. What is an element? • In the late 1600’s, experiments by early chemists began to show that matter is made up of more than 4 elements • Scientists know that all matter is made up of slightly more than 110 different substances called elements

4. What is an element? • An element is a pure substance that cannot be broken down into any other substances by either chemical or physical means • Elements are the simplest substances • Each element can be identified by its specific physical and chemical properties

5. What are examples of elements? • Aluminum which is used to make f0il and outdoor furniture, is an element • Zinc is an element which makes up pennies • Copper is another element and is used to coat pennies • Oxygen and nitrogen which makes up nearly 99% of Earth’s atmosphere are also elements

6. What is an atom? • Since the early 1800’s scientists have known that all matter is made up of atoms • An atom is the basic particle from which all elements are made • Different elements have different properties because their atoms are different • The atom has a positively charged center, or nucleus surrounded by a “cloud” of negative charge

7. The Atom

8. What happens when atoms combine? • Atoms of most elements have the ability to combine with other atoms • When atoms combine they form a chemical bond – a force of attraction between 2 atoms • Atoms can combine to form larger particles called molecules- groups of 2 or more atoms held together by chemical bonds

9. What is a compound? • In nature, most elements are found combined with other elements • A compound is a pure substance made up of 2 or more elements chemically combined in a set ratio • For example, water is a compound because it consists of the elements hydrogen and oxygen H2O

10. How is a compound represented? • A compound may be represented by a chemical formula, which shows the elements in the compound and the ratio of atoms • For example, the chemical formula for carbon dioxide (the gas you exhale) is CO2 • The number 2 below the symbol for oxygen tells you that the ratio of carbon atoms to oxygen atoms is 1 to 2 • If there is no number after the element’s symbol, the number 1 is understood

11. How is a compound represented? • If a different ratio of carbon atoms and oxygen atoms are seen in a formula you have a different compound • For example, carbon monoxide – a gas produced in car engines has the formula CO • The ratio of carbon atoms to oxygen atoms is 1 to 1

12. What happens to the properties of elements when they are chemically combined? • When elements are chemically combined they form compounds having properties that are different from those of the uncombined elements • For example, table sugar, C12H22O11, is a compound made of the elements carbon, hydrogen, and oxygen • The sugar crystals do not resemble the gases oxygen and hydrogen or the black carbon you see in charcoal

13. What is a mixture? • Elements and compounds are pure substances • Most of the materials we see everyday are not pure – they are mixtures • A mixture is made up of 2 or more substances – elements, compounds, or both – that are together in the same place but are not chemically combined

14. How do mixtures differ from compounds? • Mixtures differ from compounds in 2 ways: • Each substance in a mixture keeps its individual properties • The parts of a mixture are not combined in a set ratio • An example would be soil: • If you look at soil through a magnifying glass you would find particles of sand, clay, or even pieces of decaying plants

15. What is a heterogeneous mixture? • A mixture can be heterogeneous or homogenous • In a heterogeneous mixture you can see the different parts • A heterogeneous mixture has larger parts that are different from each other • Examples of heterogeneous mixtures are soil, a salad, tacos, vegetable soup, a toy box full of toys, or a toolbox full of nuts and bolts

16. What is a homogeneous mixture? • Homogeneous means “the same throughout” • In a homogeneous mixture, the substances are so evenly mixed that you can’t see the different parts • You might not always know that homogeneous mixtures are mixtures because you can’t tell by looking • Homogeneous mixtures can be solids, liquids, or gases • Examples are solutions such as air, sugar dissolved in water, brass, juice, milk

17. How can a mixture be separated? • Compounds and mixtures differ also in their ability to be separated • A compound can be difficult to separate into its elements because it is held together by chemical bonds • A mixture is easy to separate into its components because each component keeps its own property

18. Examples of How To Separate Mixtures • Examples of methods used to separate mixtures include magnetic attraction, filtration, distillation, and evaporation