Universe is made of matter 2.1 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

Elements 2.1 Matter  Elements – substance that cannot be broken down by chemical or physical means  Over 100 elements are known  Use symbols ex: H = hydrogen

Atoms  Smallest particles of matter 2.1 Matter  Have all the characteristics of an element Neutrons: neutral; mass = 1 amu  The nucleus is the central part of an atom and contains Protons: positive charge; mass = 1 amu  Atomic mass = number of protons AND neutrons in the nucleus

Atoms 2.1 Matter  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

Nucleus Each energy level can hold a certain number of electrons. The farther away from the nucleus, the more electrons the energy level can hold The number of electrons each level can hold is determined by using the equation 2(n 2 ) where n = the number of the energy level 1 st energy level = 2(n 2 ) = 2(1 2 ) = 2(1) = 2 electrons 2 nd energy level = 2(n 2 ) = 2(2 2 ) = 2(4) = 8 electrons 3 rd energy level = 2(n 2 ) = 2(3 2 ) = 2(9) = 18 electrons

Periodic Table 2.1 Matter  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 e - ? VALENCE! Outermost energy level! Draw a Lewis Dot structure

Isotopes  Many isotopes are radioactive and emit energy and particles.  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 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 2. Ionic bonds form between positive and negative ions. There is a transfer of electrons! 2.1 Matter 1. Covalent bonds form when atoms share electrons. 3. Metallic bonds form when metal ions share electrons.

Covalent Bond Metallic Bond

Ionic Bond