Atomic Structure

Atomic Structure : Atomic Structure Early Atomic Theory Democritus (400 BC) suggested that the world was made of 2 thing empty space and tiny, invisible particles called atoms.

Aristotle : Aristotle Aristotle believed matter was composed of 4 basic elements, water, fire, earth, and air. He was a well respected so everyone discounted Democritus’s atomic theory and believed Aristotle’s theory without question.

Slide 3 : John Dalton (early 1800s) using the experimental observations of others, Lavoisier, and Proust proposed his own atomic theory.

Dalton’s Atomic Theory : Dalton’s Atomic Theory All elements are composed of tiny particles called atoms. Atoms of the same element are identical. The atoms of any one element are different from those of another element. Isotopes of an element are not identical.

Slide 5 : Atoms cannot be divided, created, or destroyed. Atoms are divisible by a nuclear charge. Atoms of different elements can combine with one another in simple, whole number ratios to form compounds. Chemical reactions occur when atoms are joined, separated, or rearranged. However, atoms of one element are not changed into atoms of another element.

Early Research on Atomic Particles : Early Research on Atomic Particles Thomson (1867) used a cathode ray tube to prove the existence of negatively charged subatomic particles called electrons.

Cathode Rays and the Electron : Cathode Rays and the Electron Thomson investigated cathode rays using a devise called a cathode ray tube or CRT. Currents of electricity were pumped into vacuum tubes causing the tube to fluoresce. Thomason used magnets to determine the identity of the particles making up the rays. He found them to be tiny, negatively charged particles.

Robert Millikan (1909) used his oil drop experiment to prove that the charge on of an electron is -1. : Robert Millikan (1909) used his oil drop experiment to prove that the charge on of an electron is -1.

Rutherford : Rutherford Using his gold foil experiment, Rutherford proposed that the atoms is composed of a lot of empty space with, a small dense, positively charged nucleus.

Slide 13 : Thomson – used a modified cathode ray tube to prove the existence of a positively charged subatomic particle called a proton. It has equal but opposite charge to the electron (+1) and a mass 1840 times heavier than an electron.

Chadwick : Chadwick Chadwick used a device to prove that the nucleus contained neutral particles of the same mass as the proton called neutron.

Slide 15 :

Slide 16 : The atomic number is the number of protons in an atom. This number is unique for all elements and the atomic number is used to identify each element. Since atoms are electrically neutral, THE NUMBER OF PROTONS EQUALS THE NUMBER OF ELECTRONS.

Isotopes are atoms of the same element that differ in the number of neutrons in the nucleus. Isotopes of the same element have the different chemical properties.The number of neutrons determines the particular isotope of the element. : Isotopes are atoms of the same element that differ in the number of neutrons in the nucleus. Isotopes of the same element have the different chemical properties.The number of neutrons determines the particular isotope of the element.

Subatomic Particle Chart : Subatomic Particle Chart

Slide 20 : The mass number is the total number of protons and neutrons in an atom. Mass Number = protons + neutrons Mass number – protons = Number of Neutrons

Calculating Atomic Mass : Calculating Atomic Mass Atomic Mass is the weighted average of the masses of the isotopes of that element. A weighted average takes into consideration both the mass and the abundance of each isotope. The correct unit for atomic mass is amu.

Slide 24 : To calculate relative atomic mass, multiply the mass number of each isotope by its percent abundance changed to a decimal and total. (Mass #)(isotope’s relative abundance) + (Mass #)(another isotopes Rel. abund) = Relative atomic mass of the element

Slide 25 : EXAMPLE: 32.09384 amu