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2.1 Matter Universe is made of matter Matter exists in one of 3 states Solid – definite shape & volume Liquid – definite volume, no definite shape Gas – no definite volume, no definite shape 2.1 Matter Elements Elements – substance that cannot be broken down by chemical or physical means Over 100 elements are known Use symbols ex: H = hydrogen 2.1 Matter Atoms Smallest particles of matter Have all the characteristics of an element The nucleus is the central part of an atom and contains • Protons: positive charge; mass = 1 amu • Neutrons: neutral; mass = 1 amu Atomic mass = number of protons AND neutrons in the nucleus 2.1 Matter Atoms Energy levels, or shells • Surround the nucleus • Contain electrons •Electrons: negative charge, 1/1836 amu The atomic number = number of protons in the nucleus of an atom. Also tells us the number of electrons. Model of an Atom Each energy level can hold a certain number of electrons. The farther away from the nucleus, the more electrons the energy level can hold 3 2 1 The number of electrons each level can hold is determined by using the equation 2(n2) where n = the number of the energy level Nucleus 3rd energy level = 2(n2) = 2(32) = 2(9) = 18 electrons 2nd energy level = 2(n2) = 2(22) = 2(4) = 8 electrons 1st energy level = 2(n2) = 2(12) = 2(1) = 2 electrons 2.1 Matter Periodic Table Group Number = number of valence electrons in each element in that group (column) Period Number = number of energy levels containing electrons for every element in that period (row) Chemical Symbol Info Atomic number Chemical symbol Element name Atomic mass Carbon Try Your Own… • Magnesium (Mg) • Helium (He) • Sulfur (S) Ions • When an atom gains or loses electrons it becomes an ion • Gains a positive or negative charge • Example = Lithium What are the most reactive • VALENCE! • Outermost energy level! • Draw a Lewis Dot structure e? 2.1 Matter Isotopes Isotopes of an element have the same number of protons but varying numbers of neutrons. Have different mass numbers: the sum of the neutrons plus protons Many isotopes are radioactive and emit energy and particles. 2.1 Matter Why Atoms Bond Atoms are likely to form chemical bonds with one or more atoms to fill their outermost energy level (valence!) Compounds form when atoms are more stable in a combined form Most stable elements = Noble gases (group 18) 2.1 Matter Types of Chemical Bonds 1. Covalent bonds form when atoms share electrons. 2. Ionic bonds form between positive and negative ions. There is a transfer of electrons! 3. Metallic bonds form when metal ions share electrons. Covalent Bond Metallic Bond Ionic Bond