118 known elements Elements up to and including Californium (98) exist naturally; the rest have been synthesized in laboratories. Metals Metals are located to the left.  Are shiny and ductile.  Are good conductors of heat and electricity. Nonmetals Nonmetals are located to the right.  Are dull, brittle, and poor conductors of heat and electricity.  Are good insulators. Metalloids Metalloids - located along the heavy zigzag line between the metals and nonmetals.  Are better conductors than nonmetals, but not as good as metals.  Are used as semiconductors and insulators.

2 Some groups Some groups are known by common names. 7 periods18 groups A symbol  Consists of 1 or 2 letters.  Starts with a capital letter.  1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogenCa calcium F fluorine Al aluminum O oxygen Mg magnesium Some symbols are derived from Latin names: Au, (aurum) Ag, (argentum)Fe, iron (ferrum)

The Atom elements  atoms  subatomic particles locationelectrical charge Protons at the nucleushave a positive (+) charge. Neutrons at the nucleusare neutral. Electrons at a distance from the nucleushave a negative (-) charge.

The number of protons is fixed. the number of protons = The atomic number  Is specific for each element.  In the periodic table it appears above the symbol of an element.

Since ps and ns are the heavier particles (e- is very light), they are the main contributors to the mass of an atom. The number of neutrons can vary atomic symbols The mass number is used in atomic symbols, where all nuclear particles (ps and ns) are stated: H-3 H-2 H-1 Isotopes Atoms of the same element that vary in the number of neutrons (mass numbers). protons + neutrons = The mass number Hydrogen

Isotopes and Atomic Mass Atomic mass The average mass of all isotopes of an element based on their % abundance in nature, “weighted average”.

2. An atom of zinc has a mass number of 65. a. How many protons are in this zinc atom?1) 302) 353) 65 b. How many neutrons are in the zinc atom?1) 302) 353) 65 c. What is the mass number of a zinc atom that has 37 neutrons?1) 372) 653) 67 Practice 3. An atom has 14 protons and 20 neutrons. a. Its atomic number is1) 142) 163) 34 b. Its mass number is1) 142) 163) 34 c. The element is1) Si2) Ca3) Se 4. The nuclear symbol for an atom with 8 p +, 8n, 8e - 1. Match the elements to the description: a. Metals in Group 4A(14)1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn b. Nonmetals in Group 5A(15)1) As, Sb, Bi 2) N, P3) N, P, As, Sb c. Metalloids in Group 4A(14)1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb 8 O O 8 32

The energy of the electron has a minimum value and all other energy values of it are integer multiples (n) of this minimum. E = n (min. value)n= positive integer(1,2,3,4…) Electron ENERGY LEVELS Max Planck Neils Bohr nucleus n=1 n=2 n=3 n=4 Energy increases as n increases Lowest energy at n = 1 (closest to nucleus) max number of e - s = 2n 2 n=12 n=28 n=318 n=432 quantum n The name given to this minimum value is quantum and we say that energy is quantized. Therefore, the energy of an e - can only have a specific value based on the positive integer, n. Analogy: Money has a minimum value of 1 penny ($0.01) and all other coins or bills are restricted to integer values of this minimum: $ = n (0.01)n = a positive integer (1,2,3,4…) Example: you can hand someone 75 ($0.01)=$0.75 but not 75.5 ($0.01)=$0.755

If the wavelength of this radiation lies in the visible range, we see a colored light. wavelength Thermal energy = heat Electromagnetic energy = radiant energy Propagates as a wave E

ground state o Electrons in lowest available energy level = ground state. excited state o By absorbing E, the e- is raised to a higher energy level called the excited state. The photon travels in space as a wave. The energy of the wave is inversely proportional to its wavelength. photon An e- loses energy when it falls to a lower energy level and emits a photon (E carrier).

656.3 nm nm nm

In order to accommodate all the e-s, energy levels are subdivided into energy sublevels. These are identified by the letters s, p, d, and f. n=1 n=3 n=4 n=2 s s ss ppp dd f nucleus The number of sublevels = nn=11 sublevel n=22 sublevels n=33 sublevels ENERGY SUBLEVELS

n=1 n=3 n=4 n=2 sss s pp p d d f nucleus Orbitals An orbital Is a three-dimensional space around a nucleus where an electron is most likely to be found. Generally denoted by a box. Erwin Schrödinger Physicist The number of orbitals = n 2 n=11 2 =1 n=22 2 =4 n=33 2 =9

Orbitals An orbital can hold up to 2 electrons. These must spin in opposite directions. Arrows are used to represent these e-s.

15 Practice 5. In each of the following energy level changes, indicate if energy is: 1) absorbed2) emitted 3) not changed. a. An electron moves from the first energy level (n = 1) to the third energy level (n = 3). b. An electron falls from the third energy level to the second energy level. c. An electron moves within the third energy level. 6. The number of A. electrons that can occupy a p orbital is1) 12) 23) 3 B. p orbitals in the 2p sublevel is1) 12) 23) 3 C. d orbitals in the n = 4 energy level is1) 12) 33) 5 D. electrons that can occupy the 4f sublevel is1) 22) 63) Indicate the type and number of orbitals in each of the following energy levels or sublevels: a.) 3p sublevel b. ) n = 2 c.) n = 3d.) 4d sublevel

16 n=1 n=3 n=4 n=2 s s ss ppp dd f nucleus Electron Configurations electron configurations An electron configurations is a shorthand notation describing an electron position in an atom Take C as an example:total of 6 e Energy level

The Aufbau (“Build-up”) Principle (from the German aufbauen) Iron 26 e- 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 energy level sublevel number of electrons The order of filling various electron subshells with electrons follows the same order given by the arrows in this diagram. 4s lower than 3d due to sublevel overlap 1s 2s 2p 3s 3p 3d4s Ar1s 2 2s 2 2p 6 3s 2 3p 6 K1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Ca1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Sc1s 2 2s 2 2p 6 3s 2 3p 6 3d 1 4s 2 Ti1s 2 2s 2 2p 6 3s 2 3p 6 3d 2 4s 2

Exceptions to the Aufbau order In describing the ground state electron configuration the guiding idea is that it corresponds to an isolated atom in its lowest total energy. 1. The orbital energies depend on a number of factors such as nuclear charge and interactions of electrons in different occupied orbitals. 2. The energy scale varies with atomic number. In other words, all atoms of a given element have the same set of energy levels, but atoms of different elements have different sets. 3. Some orbitals are very close together, so their order can change, depending on the occupancies of other orbitals. filled or half-filled The only exceptions you are asked to remember are those based on the special stability of filled or half-filled d-orbitals.

19 Abbreviated Configurations An abbreviated configuration shows  The symbol of the noble gas in brackets that represents completed sublevels.  The remaining electrons in order of their sublevels, Example: Chlorine has a configuration of 1s 2 2s 2 2p 6 3s 2 3p 5 The abbreviated configuration for chlorine is [Ne] 3s 2 3p 5 [Ar] 4s 2 3d 6 Iron 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

C 1s 2 2s 2 2p 2 Orbital Diagrams diagram Orbitals as boxes. diagram Electrons as vertical arrows. The Pauli Exclusion Principle Electrons in the same orbital with opposite spins (up and down vertical arrows). Hund’s rule Fill orbitals in sublevels of the same type with one electron until half full, then pair up using opposite spins. Friedrich HundWolfgang Pauli

Sublevel Blocks O1s 2 2s 2 2p 4 Ca1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 O Ca

Example: Phosphorus has 5 valence electrons. P Group 5A(15) 1s 2 2s 2 2p 6 3s 2 3p 3 n =1 n=2 n=3 Periodic Trends valence electrons The valence electrons  are the electrons in the outermost, highest energy level  are related to the Group number of the element  determine the chemical properties of the elements

 Convenient way of representing valence electrons using dots around the symbol of the element. · · · Mg· or Mg· or · Mg or · Mg ·  The same for all members in a group. · Be · · Mg · · Ca · · Sr · · Ba ·  Groups 1A(1) to 4A(14) use single dots · · Na · · Mg · · Al · · C· ·  Groups 5A(15) to 7A(17) use pairs and single dots. · · · · · P· : O· · An electron-dot symbol

12. a. X is the electron-dot symbol for1) Na2) K3) Al b. X is the electron-dot symbol for1) B2) N3) P 11. State the number of valence electrons for each. a. 1s 2 2s 2 2p 6 3s 2 3p 1 b. 1s 2 2s 2 2p 6 3s 2 c. 1s 2 2s 2 2p 5 Practice 9. Write the orbital diagrams for a. nitrogen b. oxygen 8. Write the electron configuration and abbreviated configuration for the following elements: a. Sb. K 10. State the number of valence electrons for each. a. Calcium b. Group 6A (16) c. Tin