Atomic Structure & Periodic Table Introduction Physical Science JPHancock

The Atom Basic building block of all matter Elements on periodic table are represented as one neutral atom Chemical symbols are abbreviated ways of representing elements C, H, N, O Na, Cl, Ne, Cu NaCl, H2O, CO2

Parts of the Atom Protons= (+) charge Neutrons= (0) charge Electrons= (-) charge Quarks= smallest particles arranged in groups of threes to make p+, e-, or n0

History of the Atomic Model Aristotle 350BC Matter made up of earth, air, fire, and water Democritus 400 BC Matter cannot be divided indefinately. “atomos = uncuttable” Dalton 1803 “Billard Ball Model” Atom solid and undivisible

“Plum Pudding Model” – a (+)sphere with (-) particles embedded Thomson 1904 “Plum Pudding Model” – a (+)sphere with (-) particles embedded Rutherford 1911 Most of the mass in a (+) nucleus surrounded by (-) electrons Bohr 1913 (+) protons & neutral neutrons in nucleus e- are in shells and can jump to higher levels with energy

Rutherford Experiment

Electron Cloud Model-1926 “Probability Cloud” Electrons orbit the nucleus in energy levels or orbits. Why is it considered a “probability cloud”?

EVOLUTION OF ATOM

PERIODIC TABLE

The number of neutrons = mass number –atomic number In a neutral atom the number of e- and number of p+ are equal Every atom of the same element has the same number of protons MASS NUMBER =ATOMIC MASS

ISOTOPES Atoms of the same element with different numbers of neutrons

Atomic Mass Units Do we now know how much atoms really weigh, in pounds or grams? Yes, but we don't normally use those units for measuring the mass of an atom. It's much more convenient to use something called the atomic mass unit, or amu.

Using AMU is simplier! One gram is about 600,000,000,000,000,000,000,000 amu (that's 600 sextillion, or a 6 followed by 23 zeros). A pound is just shy of 300 septillion amu--that is, 300,000,000,000,000,000,000,000,000. (26 zeros there.)

Periodic Table 1869 Dmitri Mendeleev arranged the elements in order of their increasing atomic masses He discovered a pattern and was able to give rise to the modern periodic table

Mendeleev’s Periodic Table

PERIODIC LAW The properties of elements are a periodic function of their atomic number The properties change in a repeated pattern as we move across or down the periodic table Elements are arranged by changes in physical and chemical properties

MODERN PERIODIC TABLE 1913 Henry G.J. Moseley Arranged the periodic table based on increasing atomic numbers PERIODS or Series –horizontal rows 1-7 GROUPS or Families-vertical columns 1-18 with similar properties

Properties of Groups Elements of same group have same # valence electrons Valence electrons- are the e- in the outermost energy level Important role in chemical reactivity Electrons closer to the nucleus have lower energy than those farther away

Properties of Series Horizontal rows Periods or Series Adjacent elements in each horizontal row(period)differ in both chemical and physical properties but the properties change in a regular way across each period

Ionization Energy Amount of energy needed to remove the outer electrons As you move right to left the radius of the nucleus increases meaning the size(distance) between the nucleus and electrons is greater As you move left to right the radius decreases meaning the electrons are valence electrons closer to the nucleus, held tighter and require more energy to remove

Atomic Radii

Electron Dot Diagrams Used to represent valence electrons in bonding