Dmitri Mendeleev order elements by atomic mass saw a repeating pattern of properties Periodic Law – When the elements are arranged in order of increasing relative mass, certain sets of properties recur periodically used pattern to predict properties of undiscovered elements where atomic mass order did not fit other properties, he re-ordered by other properties 1834 - 1907

Periodic Table Pattern H nm H2O a/b 1 H2 Li m Li2O b 7 LiH Be m/nm BeO a/b 9 BeH2 nm B2O3 a 11 ( BH3)n B nm CO2 a 12 CH4 C nm N2O5 a 14 NH3 N nm O2 16 H2O O nm OF2 19 HF F left  right across a row (period) increasing atomic mass (not relative mass); organized based on their activity and properties

Periodic Table Pattern H nm H2O a/b 1 H2 Li m Li2O b 7 LiH Be m/nm BeO a/b 9 BeH2 nm B2O3 a 11 ( BH3)n B nm CO2 a 12 CH4 C nm N2O5 a 14 NH3 N nm O2 16 H2O O nm OF2 19 HF F Na m Na2O b 23 NaH m MgO b 24 MgH2 Mg m Al2O3 a/b 27 (AlH3) Al nm/m SiO2 a 28 SiH4 Si nm P4O10 a 31 PH3 P nm SO3 a 32 H2S S nm Cl2O7 a 35.5 HCl Cl up  down column; similar properties; how the elements react with H and O some gaps were left in table for undiscovered elements; properties of these elements were predicted.

Mendeleev's Predictions for Ekasilicon (Germanium) 14 28.09 32 72.61 Ge Sn 50 118.71

PERIODIC TABLE Non-metals Metals Metalloids

PROPERTIES OF METALS & NON-METALS Mostly solid Can be solid, liquid or gas Have shiny appearance Have dull appearance Good conductors of heat & electricity Poor conductors of heat & electricity Malleable & ductile Brittle (if solid) Lose electrons Gain or share electrons

Metals Non-metals

METALLOIDS Metalloids are elements that possess some properties of metals and some of non-metals. The most important metalloids are silicon (Si) and germanium (Ge) which are used extensively in computer chips.

Metalloids Properties of Silicon shiny conducts electricity brittle

PERIODIC TABLE Metallic character decreases going across a period. Metallic character increases going down a group F Least metallic element Cs Fr Most metallic elements

PERIODIC TABLE Seven elements exist as diatomic molecules. All others exist as monatomic (single atom).

PERIODS & GROUPS The periodic table is composed of periods (rows) and groups or families (columns). Elements in the same family have similar properties, and are commonly referred to by their traditional names.

PERIODS & GROUPS Group 2 elements are called alkaline-earth metals. These metals are less reactive than alkali metals. The group of metals in between the main group elements are called transition metals. Halogens are the most reactive nonmetals, and occur in nature only as compounds. Noble gases are un-reactive gases that are commonly used in light bulbs. Elements in groups 1-2 and 13-18 are referred to as main-group or representative groups. Alkali metals are soft metals that are very reactive. They often react explosively with other elements.

Important Groups - Hydrogen nonmetal colorless, diatomic gas very low melting point & density reacts with nonmetals to form molecular compounds HCl is acidic gas and H2O is a liquid reacts with metals to form hydrides (negative ion of hydrogen = H-) metal hydrides react with water to form H2 (Metal-H + H2O H2 + metal-OH) (NaH + HOH H2 + NaOH)

Important Groups – IA, Alkali Metals hydrogen usually placed here, though it doesn’t belong soft, low melting points,low density flame tests ® Li = red, Na = yellow, K = violet very reactive, never find uncombined in nature tend to form water soluble compounds lithium sodium potassium rubidium cesium

Important Groups – IIA, Alkali Earth Metals harder, higher melting, and denser than alkali metals flame tests ® Ca = red, Sr = red, Ba = yellow-green reactive, but less than corresponding alkali metal form stable, insoluble oxides from which they are normally extracted oxides are basic = alkaline earth reactivity with water to form H2, beryllium magnesium calcium strontium barium

Important Groups – VIIA, Halogens nonmetals F2 & Cl2 gases; Br2 liquid; I2 solid all diatomic very reactive react with metals to form ionic compounds HX (X = halogen) are all acids HF weak < HCl < HBr < HI fluorine chlorine bromine iodine

Important Groups – VIIIA, Noble Gases all exist as gases at room temperature, very low melting and boiling points very unreactive, practically inert very hard to remove electron or add an electron

Atomic number (Z) = # of protons Mass number (A) = # of p+ + # of n0 ATOMIC STRUCTURE The general designation for an atom is shown below: Atomic number (Z) = # of protons Mass number (A) = # of p+ + # of n0 # of n0 = A - Z

Charged Atoms The number of protons determines the element! all sodium atoms have 11 protons in the nucleus In a chemical change, the number of protons in the nucleus of the atom doesn’t change! no transmutation during a chemical change!! during radioactive and nuclear changes, atoms do transmute Atoms in a compound are often electrically charged, these are called ions

ELEMENTS & IONS An ion (charged particle) can be produced when an atom gains or loses one or more electrons. Metals form cations A cation (+ ion) is formed when a neutral atom loses an electron Cations are named the same as the parent atom 5.1

ELEMENTS & IONS Anions are named by using the root of the parent atom’s name and changing the ending to –ide. Chlorine changes to chloride Non-metals form anions An anion (- ion) is formed when a neutral atom gains an electron 5.1

Ion Charge & the Periodic Table Every element wants to be like the noble gases wants 0 or 8 valence electrons valence e- (outer electron shell used for bonding) He has zero valence e-

ELEMENTS & IONS elements of Group IA have a +1 charge elements of Group VIA have a -2 charge elements of Group IIA have a +2 charge elements of Group VIIA have a -1 charge elements of Group VA have a -3 charge For main-group elements, the charge of ions are very characteristic of the group numbers.

Structure of the Nucleus (1877-1956) Frederick Soddy discovered that the same element could have atoms with different masses, which he called isotopes there are 2 isotopes of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu The observed mass is a weighted average of the weights of all the naturally occurring atoms the atomic mass of chlorine is 35.45 amu

Isotopes Atomic mass - The average mass for a given element all isotopes of an element have the same number of protons isotopes of an element have different masses isotopes of an element have different numbers of neutrons isotopes are identified by their mass numbers protons + neutrons

ISOTOPES Isotopes of an element have the same atomic number (Z), but a different mass number (A). Atoms of the same element that possess a different number of neutrons are called isotopes. The 3 isotopes of Hydrogen

ISOTOPES & ATOMIC MASS The mass of an atom is measured relative to the mass of a chosen standard (carbon-12 atom), and is expressed in atomic mass units (amu). The average atomic mass of an element is the mass of that element’s natural occurring isotopes weighted according to their abundance. Therefore the atomic mass of an element is closest to the mass of its most abundant isotope.

4.8 Isotopes: Natural Abundance Isotopes of neon   Naturally occurring neon contains three different isotopes: Ne-20 (with 10 protons and 10 neutrons), Ne-21 (with 10 protons and 11 neutrons), and Ne-22 (with 10 protons and 12 neutrons).

Example 1: Determine the number of protons, electrons and neutrons in a chlorine atom . # of protons = 17 (Z) # of electrons = 17 (= p+) # of neutrons = 18 (35 - 17)

Example 2: Which two of the following are isotopes of each other? Isotopes of an element have the same atomic number, but a different mass number

Example 3: Based on the information below, which is the most abundant isotope of boron (atomic mass = 10.8 amu) ? Isotope 10B 11B Mass (amu) 10.0 11.0 Atomic mass of an element is closer to the mass of the more abundant isotope

CALCULATING MASS FROM ISOTOPIC DATA Isotope Mass (amu) Abundance (%) 107Ag 106.91 51.84 109Ag 108.90 48.16 (106.91) (0.5184) = 55.42 amu (108.90) (0.4816) = 52.45 amu 107.87 amu

Mass Number is Not the Same as Atomic Mass the atomic mass is an experimental number determined from all naturally occurring isotopes the mass number refers to the number of protons + neutrons in one isotope natural or man-made

THE END