Chapter 5 – Atomic Structure Atoms Structure of An Atom Distinguish Between Atoms The Periodic Table

Ch 5.1 Atoms Democritus of Abdera (Greece) 4 th Century BC Coined the term “atom” Could not prove because no scientific research was being done

John Dalton ( ) Conducted research as to the ratios of elements in compounds From the research he came up with Daltons Atomic Theory

Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms.

Dalton’s Atomic Theory 2. Atoms of the same element are identical. The atoms of one element are different from those of any other element.

Dalton’s Atomic Theory 3. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole number ratios to form compounds.

Dalton’s Atomic Theory 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Atom The smallest particle of an element that retains the properties of that element.

Just How Small is an Atom A pure copper coin about the size of a penny has 2.4 x atoms 2,400,000,000,000,000,000,000,000 atoms Earths population is only 6 x 10 9 people

Just How Small is an Atom A 1cm long line of copper atoms has 100,000,000 atoms

Ch 5.2 Structure of the Nuclear Atom Particle Accelerators are used to smash particles at speeds near the speed of light into each other in order to break them apart A bubble chamber is used to track the paths of the broken particles Cant ever see the actual particles

Electrons Negatively charged subatomic particle e-

Electrons J.J. Thomson ( ) discovered electrons in 1897 Invented cathode ray tubes (used in TVs)

Electrons Robert Millikan (1868 – 1953) Determined an accurate mass of an electron Mass 1/1840 of a hydrogen atom

Protons E. Goldstein (1886) discovered protons in a cathode ray tube Protons are positively charged Mass is 1840 times an electron

Neutrons James Chadwick (1932) discovered neutrons No Charge Mass the same as a proton

ParticleSymbolChargeRelative Mass Actual Mass (g) Electrone-1-1/ x Protonp+p x Neutronn0n x10 -24

Atomic Nucleus Rutherfords Gold Foil Experiment Shot rays of alpha particles at thin gold foil Most passed straight through Some bounced off at large angles Some bounced straight back Suggested that an atom is mostly empty space with most of the mass and the positive charge in the center (nucleus)

Ch 5.3 Distinguish Between Atoms Atoms are made up of Electrons Protons Neutrons Nucleus contains protons and neutrons

Atomic Number The number of protons in the nucleus of an element Every element has a different atomic number

Atomic Number The number of protons equals the number of electrons Protons are positive, electrons are negative, therefore the total net charge of an atom is 0

Mass Number The number of protons and neutrons. Number of neutrons equals mass number minus atomic number

Mass Number The number of protons does not always equal the number of neutrons Oxygen Beryllium

Isotopes There are different types of neon What is different?

Isotopes All of the neon's have the same number of protons and electrons, but different number of neutrons Ne-20 has 10 Ne-21 has 11 Ne-22 has 12

Isotopes Atoms that have the same number of protons and electrons but different numbers of NEUTRONS. This also creates a different mass number for each.

Hydrogen

Atomic Mass AMU (Atomic Mass Units) defined as 1/12 the mass of carbon-12 or 1 amu.

Atomic Mass The weighted average mass of the atoms in a naturally occurring sample of the element. Based on the percent of each isotope present on earth.

Atomic Mass Chlorine 35 – 75.77% Chlorine 37 – % Average Mass based on Percents =