Chapter 17 Properties of atoms & the periodic table https://www.youtube.com/watch?v=rz4Dd1I_fX 0

Section 1: structure of the atom Each element has a chemical symbol Chemical symbol: consists of one capital letter OR one capital letter + one or two lower case letters H Na System is universal Everyone knows what they mean!

Atomic components Atom- the smallest piece of matter that retains the properties of the element Atoms are composed of protons, neutrons, and electrons Protons and neutrons are found in the nucleus Protons- particles with a charge of +1 Neutrons- neutral particles (no charge) Electrons- particles with a charge of -1

Models of the atom Difficult to visualize This is what models are for! Democritus (B.C.) 1800s John Dalton proved atoms existed Solid spheres The model of the atom is ever changing

Electron cloud is much larger than the nucleus The electron cloud Electrons are found in an electron cloud Electron cloud- the area around the nucleus where electrons are likely found Electron cloud is much larger than the nucleus

Review What is the charge of a proton? What is the charge of a neutron? What is the charge of an electron? What is in the nucleus? What determines the atomic number? Where does the mass of an atom come from?

Section 2: Masses of atoms Most of the mass of an atom is in the nucleus Protons and neutrons are approx. the same size Electrons are much smaller

Atomic number Atomic number—the number of protons in an atom. (always a whole number) Atoms of different elements have different #’s of protons & different atomic #’s. The atomic # of an element is on the periodic table

Mass number Mass Number—the sum of the # of protons & the # of neutrons Mass # = # of neutrons + atomic # If you know mass # & atomic # you can find the # of neutrons. # of neutrons = Mass # - Atomic # Not all atoms of the same element have the same # of neutrons

isotopes Different isotopes of elements have different properties. Isotopes—atoms of the same element with different numbers of neutrons Different isotopes of elements have different properties. You can distinguish isotopes by writing the name of the element followed by the mass #. Ex. Carbon-12 and Carbon-14 Each element has an average atomic mass.

Atomic mass Average atomic mass (or atomic mass)—the weighted average mass of the mixture of isotopes. (found on the periodic table) Atomic mass is always closest to the most abundant isotope.

Section 3: The periodic table Periodic Table— an organized list of all known elements that are arranged according to their properties The 1st person to organize elements was Dmitri Mendeleev in the 1800s Mendeleev organized the elements by their atomic mass and left spaces for unknown elements.

The modern periodic table Mendeleev’s table was mostly correct, but it is more accurate to organize elements in order of increasing atomic number.

groups Groups (or families)— vertical columns on the periodic table. They are numbered 1-18. Elements in each group have similar properties.

periods Periods—horizontal rows of elements on the periodic table. Periods are numbered 1-7 Elements increase by one proton as you move from left to right across a period.

Electrons and the periodic table The periodic table organizes elements based on where their electrons are located. 1 Electrons (e-)—are located in different energy levels around the nucleus. 2 Elements in the same group have electrons arranged similarly which gives them similar properties. 3

Electron shells The number of energy levels or electron shells is determined by the period number. Period 1: 1 electron shell and can hold 2 e- Period 2: 2 electron shells & can hold 8 e- Period 3: 3 electron shells & can hold 8 e- As you move down the periodic table, 1 electron shell is added each time. The outer electron shell must be full (usually with 8 e-) to be stable.

Electron dot diagrams You can show the number of electrons in the outermost electron shell by using an electron dot diagram. Dot diagrams use valence electrons which are the electrons in the outer electron shell. Electron Dot Diagram—uses the symbol of the element and dots to represent the valence electrons.