Pure Substances and Mixtures

1. Pure Substances and Mixtures

2. Pure substances cannot be broken down by physical means.

3. Pure substances contain only one kind of molecule. • Molecules are small groups of atoms that make up matter. Example: Water is a molecule of two hydrogen atoms, and one oxygen atom • Atoms are the smallest particles of elements

4. Two types of pure substances: • Elements – pure substance made of only one kind of atom • Compounds – pure substances made of two or more different kinds of elements joined together • Compounds cannot be separated by physical means • Compounds are joined in definite proportions.

5. Mixtures – combination of 2 or more different kinds of substances ( molecules) • In a mixture, each molecule keeps its own identity. • Mixtures can be separated by physical means.

6. Two types of mixtures: • Homogeneous mixture – combination of substances in which the appearance is the same throughout; also called a solution. • Examples: salt water, sugar water

7. Heterogeneous mixture – made of different substances that can be seen – does not appear the same throughout. • Examples – salad, cereal, pizza

8. Atoms and Elements • Facts about atoms and elements: • Atoms are the basic building blocks of all matter (the smallest particle of matter) • There are different kinds of atoms.

9. Each kind of atom is an element. • Elements are pure substances that cannot be broken down into simpler substances by ordinary chemical means.

10. Parts of an Atom: • Nucleus – central dense core of the atom. It is made of: • Protons – positively charged particles • Neutrons – neutrally charged particles • Electron cloud – surrounds the nucleus of the atom • Electrons – negatively charged particles found in the electron cloud

11. Atomic models – used to represent the atom; the following is needed to make an atomic model • Atomic number – number of protons in the nucleus of an atom • Atomic mass – equal to the number of protons and the number of neutrons in the nucleus of the atom

12. Making atomic models – the following information is needed for an atomic model • # of protons = the atomic number • # of neutrons = the atomic mass – atomic #

13. # of electrons = 3 of protons • Energy levels – electrons surround the nucleus in energy levels • Rules for energy levels: • 1st energy level contains no more than 2 electrons • 2nd energy level contains no more than 8 electrons • 3rd energy level contains no more than 18 electrons

14. Last energy level contains no more than 8 electrons • Valence electrons is the name given to electrons in the last energy level of the atom. There will NEVER be more than 8 valence electrons • Elements in columns 1A through VIIIA: the number of valence electrons can be determined by the column number; 1A has 1 valence electron, IIA has 2 valence electrons, etc.

15. Electron Dot Configurations • Electron Dot configurations – are used to represent atoms; 2 things are needed: • Symbols of elements • Valence electrons

16. Draw the electron dot configuration of the following elements: • H Mg B C • N O F He Kr

17. IV. Compounds – two or more elements held together by a chemical bond. • Chemical bond – the point at which elements are joined in a compound; the bond is made by either sharing or giving and taking valence electrons. • Chemical formula – the recipe for a compound

18. Bonds for compounds: Sodium Chloride Water