What is an ATOM? Basic unit of ALL matter

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1 What is an ATOM? Basic unit of ALL matter Has two parts: 1. Nucleus Protons (positively (+) charged particles) Neutrons (neutrally (o) charged particles) 2. Electron Cloud Electrons (negatively (-) charged particles) MOSTLY EMPTY SPACE!

2 Where are the Electrons in the Electron Cloud? We don t really know The electron cloud shows us where we are MOST LIKELY to find electrons - based on probability calculations Usually shown as shaded rings around the nucleus. Each ring represents an energy level.

3 Electrons Moving Energy Levels Photon = tiny packet of energy When an electron gains a photon, the electron increases in energy level/jumps farther away from the nucleus. When electron releases the photon, the electron falls closer to the nucleus and LIGHT is given off Color of light depends on how much energy is released when the electron jumps down (or how far the jump is)

4 What are Valence Electrons? Electrons in the outermost energy level (farthest away from the nucleus) Valence electrons: 1. Determine chemical properties 2. Participate in bonding

5 What are Elements? A substance that cannot be broken down into a simpler substance. The identity of an element is determined by the number of protons in an atom s nucleus! Ex. Helium - 2 protons Oxygen - 8 protons Gold - 79 proton If the number of protons changes, the ELEMENT changes.

6 What are Elements? (cont.) Each element has a SYMBOL that represents it. - One or two letters - Ex. H, S, Li, Mn, Fe Each element has an ATOMIC NUMBER - Same as the number of proton in the nucleus Each element has a MASS NUMBER - Sum of the particles in the nucleus - Mass # = # Protons + # Neutrons - Units are amu (atomic mass unit) - Why don t we count electrons in the mass number?

7 Isotopes Elements identities are determined by the number of protons they have, so they can have different numbers of neutrons and still be the SAME element. Isotopes have different mass #s. Explains why our mass numbers on the periodic table are not whole numbers! Examples of Hydrogen Isotopes: Protium (Atomic Mass = 1) Deuterium (Atomic Mass = 2) Tritium (Atomic Mass = 3)

8 Isotopes (continued) Can be written TWO ways!

9 To calculate # neutrons Mass # - # protons = # neutrons Ex. Oxygen = 9 neutrons

10 Ions Does NOT have equal numbers of protons and electrons Positive (+) or negative (-) charge If the atom GAINS an electron, it becomes an ANION If the atom LOSES an electron, it becomes a CATION

11 Candium Lab

12 Why do atoms gain/lose electrons? An outer shell of 8 makes an atom feel great! Atoms are most stable when they have complete/full outermost energy levels. An atom with only a few electrons will lose them and become a cation. Atoms that are close to complete shells will gain electrons and become an anion.

13 Periodic Table Organization There are currently 118 elements!!!! Period - horizontal rows Group - vertical columns Organized by increasing atomic number / number of protons in the nucleus

14 Periodic Table Organization (cont.) Elements in the same GROUP (column) have similar properties Examples: Group 1 - Alkali metals - explode in water Group 18 - Noble gases - don t react with the other elements

15 WHY?! Why are grouped elements similar? They have the same number of valence electrons! Since valence electrons are the ones that participate in bonding and determine chemical reactivity, so elements with the same number of valence electrons will have similar properties.

16 There are 3 FAMILIES: Metals, Nonmetals, and Metalloids Families are elements that are similar to each other

17 METALS Left side of the periodic table - MOST of the elements on the PTable are in this family Group 1 - Alkali metals Group 2 - Alkaline-earth metals Groups Transition Metals

18 Alkali Metals 1 valence electron Soft and shiny VERY reactive Usually found in compounds (ex. NaCl)

19 Alkaline-Earth Metals 2 valence electrons Harder and denser than the alkali metals Reactive (but not as reactive as the alkali metals) Found in sea animal shells and medicines

20 Transition Metals Complex electron arrangements Can be stretched (ductile) and shaped (malleable)

21 NONMETALS - Top-right corner of the periodic table - Plentiful on earth Group 17 - Halogens Group 18 - Noble Gases

22 HALOGENS 7 valence electrons VERY reactive Usually found as gases Only group that contains solids, a liquid, and gases at normal conditions

23 NOBLE GASES 8 valence electrons (full outer shell) Inert (non-reactive)

24 SEMI-CONDUCTORS/METALLOIDS - Non-metals with some properties of metals - ONLY SIX: - Boron (B) Silicon (Si) Germanium (Ge) Arsenic (As) Antimony (Sb) Tellurium (Te) - They can conduct heat and electricity under CERTAIN conditions (hence the name, semi-conductors)