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Pure Substances and Mixtures

Pure Substances and Mixtures. Pure substances cannot be broken down by physical means. 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

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Pure Substances and Mixtures

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  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

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