THE PERIODIC TABLE

THE SEARCH FOR THE PERIODIC TABLE 1860 – 60 elements known – organized into groups w/similar properties – also used atomic masses 1871 – Mendeleev’s Periodic Table – found that physical properties of elements repeated in a periodic (repeating) fashion if organized by increasing atomic mass – elements w/similar properties were placed in the same vertical column – similar properties repeat as you move across horizontal rows w/increasing atomic mass table showed periodicity  the tendency to recur at regular intervals when the table was finished there were some “holes” – said these were undiscovered elements -made predictions about properties – when later discovered predictions were close to perfect

when finished Mendeleev found that tellurium didn’t “fit” by atomic mass into the correct column for properties – solved this problem by saying the atomic mass must have been incorrect Mendeleev based his table on atomic mass and similar properties – as our knowledge of the structure of the atom has increased we have been able to explain the problem he found with tellurium the modern periodic table is based on increasing atomic number no mass

THE MODERN PERIODIC TABLE based on increasing atomic number (number of p + ) and grouped according to similar properties this arrangement supports periodic law  physical and chemical properties of the elements repeat in a regular pattern when they are arranged in order of increasing atomic number Parts of the periodic table – Groups or Families – vertical columns – numbered 1-18 – share similar properties - ex: reactivity, e- configuration oxidation # Periods – horizontal rows – show periodic properties Nonmetals – right side of the table – lack luster - do not conduct heat or electricity – brittle when solid – most are gases at room temp – gain e - in chem rxns

Metals – left side of the table – have luster (shiny), conduct heat and electricity, are malleable (able to be flattened) and ductile (can be drawn out into wire) – have high mp - all are solids at room temp except Hg – give away e - in chem rxns Metalloids – form a zig zag line separating nonmetals and metals – have chemical and physical properties of both metals and nonmetals – many are used in semiconductors Transition Metals – middle of the table – tend to be hard solids w/high mp and bp – most differences among these metals are in their physical properties – can form ions w/multiple charges Lanthanides – actually part of the transition metals but printed below for convenience – naturally occurring but rare Actinides – radioactive – none beyond U occur in nature – all manmade

ELEMENTAL PROPERTIES - Hydrogen – unique – put in group one b/c it has 1 valence e - but acts like both a metal and a nonmetal – does NOT really belong to any group – can either give away or accept one e - in chem. rxns Group 1 – Alkali Metals – tend to lose 1 e - in chem rxns – form ions w/a +1 charge - soft, dull metals – usually found in cmpds in nature – pure elements must be stored under oil to prevent rxn w/oxygen – good conductors of heat and electricity Group 2 – Alkaline Earth Metals – tend to lose 2 e - in chem rxns – form ions w/a +2 charge - harder, shiny metals – not easily dissolved in water

Group 14 – The Carbon Group – contains nonmetals, metalloids, and metals – carbon is unique – Carbon – can form an almost infinite number of cmpds – basic element of life – will always form 4 covalent bonds Group 17 – Halogens – name means “salt former” – tend to gain 1e - in chem rxns and are VERY reactive nonmetals and will usually be found in cmpds w/group 1 elements – form ions w/a –1 charge Group 18 – Noble Gases – colorless and unreactive due to their full outer energy levels

What information can we get from the periodic table? Each symbol is located in a box with info about the element - element symbol and name - atomic number (whole number and smaller of 2 #’s given) number of p + - if atom is neutral the # of p + = # of e - - atomic mass (decimal number and larger of 2 #’s given) – also called mass number = # of p + + # of n 0 – remember that isotopes have a different mass number this is b/c they have a different # of n 0 – mass is measured in atomic mass units (amu) which is equal to the mass of a p +

each element w/in a group has the same # of valence e - – Group 1 – 1 valence e - – Group 2 – 2 valence e - * for groups 1 and 2 the group # is the # of valence e - – Group13 – 3 valence e - *for groups 13 – 18 the second digit is the # of valence e- – Group 14 – 4 valence e - – Group 15 – 5 valence e - – Group 16 – 6 valence e - – Group 17 – 7 valence e - – Group 18 – 8 valence e - b/c the groups have the same number of valence e - they share similar chemical properties

PERIODIC TRENDS - Atomic radius – ½ the diameter of an atom - increases down a group - decreases across a period - Ion radius – ½ the diameter of the ion (charged particle) - metals tend to lose e - to form positive ions (cations) - radius of ion is SMALLER than neutral atom - nonmetals tend to gain e - to form negative ions (anions) - radius of ion is LARGER than neutral atom

- Ionization energy – energy required to remove an e - from an atom – metals have low IE b/c they want to give up e -, nonmetals have high IE b/c they want to accept e - - decreases down a group - increases across a period - Electronegativity – the ability of an element to attract e - in a chemical bond - decreases down a group - increases across a period