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 Atoms are the smallest particles of elements

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.

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.

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

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

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.

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

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

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

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

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

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.

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

Draw the electron dot configuration of the following elements: HMgB C NOF HeKr

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

Sodium Chloride Water Bonds for compounds: