Chemistry I Mr. Patel SWHS

Learn Major Ions Defining the Atom (4.1) Subatomic Particles (4.2) Atomic Structure (4.2) Ions and Isotopes (4.3) Nuclear Chemistry (25.1)

Atom – the smallest particle of an element that retains its identity Can not see with naked eye Nanoscale (10 -9 m) Seen with scanning tunneling electron microscope

Democritus was a Greek to first come up with idea of an atom. His belief: atoms were indivisible and indestructible. = WRONG! Atom comes from “atmos” - indivisible

2000 yrs later, John Dalton used scientific method to transform Democritus’s idea into a scientific theory Dalton put his conclusions together into his Atomic Theory (4 parts)

1. All elements are composted of tiny, indivisible particles called atoms.

2. Atoms of the same element are identical. Atoms of different elements are different

3. Atoms of different elements can physically mix or chemically combine in whole number ratios.

4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element can never be changed into atoms of another element due to a chemical reaction.

Particle with negative charge Discovered by J.J. Thomson Used cathode ray (electron) beam and a magnet/charged plate. Millikan found the charge and mass

An atom is electrically nuetral If there is a negative particle then there must be positive particle Proton – particle with positive charge Chadwick discovered neutron – neutral charge

Electrons distributed in a sea of positive charge Plum Pudding Model

Performed Gold-Foil Experiment Beam of Alpha particles with positive charge shot at thin piece of gold foil Alpha particles should have easily passed through with slight deflection due to positive charge spread throughout. Results: Most particles went straight through with no deflection. Some were deflected at large angles.

The nucleus is the central part of the atom containing protons and neutrons Positive charge Most of the mass Electrons are located outside the nucleus Negative charge Most of the volume

An element is defined only by the number of protons it contains Atomic Number – number of protons Number of protons = number of electron For a neutral element

1. Zinc (Zn) 2. Iron (Fe) 3. Carbon (C) 4. Uranium (U)

Nucleus contains most of the mass Mass Number – total protons and neutrons Number of neutron = Mass # – Atomic #

1. Lithium (MN = 7) 2. Nitrogen (MN = 14) 3. Fluorine (MN = 19) ** MN = Mass Number 1. 3 p +, 3 e -, 4 n p +, 7 e -, 7 n p +, 9 e -, 10 n 0

Different element: different number of protons Ions – same number of proton, different number of electrons Isotope – same number of proton, different number of neutrons Different Mass Numbers

Nuclear Notation Write the element symbol On left side, superscript = Mass Number On left side, subscript = Atomic Number Isotope –Hyphen Notation Write full name of element On right side, put a dash On right side put Mass Number after dash Hydrogen - 3

Atomic Mass Unit (amu) – one-twelfth of the mass of the carbon-12 atom Different isotopes have different amu (mass) and abundance (percentage of total) Atomic Mass – weighted average mass of the naturally occurring atoms. Isotope Mass Isotope Abundance

Because abundance is considered, the most abundant isotope is typically the one with a mass number closest to the atomic mass. Example, Boron occurs as Boron-10 and Boron-11. Periodic Table tells us Born has atomic mass of amu. Boron-11 must be more abundant

Convert the Percent Abundance to Relative Abundance (divide by 100) Multiple atomic mass of each isotope by its relative abundance Add the product (from step above) of each isotope to get overall atomic mass.

Radioactivity – nucleus emits particles and rays (radiation) Radioisotope – a nucleus that undergoes radioactive decay to become more stable An unstable nucleus releases energy through radioactive decay.

Nuclear force – the force that holds nuclear particles together Very strong at close distances Of all nuclei known, only a fraction are stable Depends on proton to neutron ratio This region of stable nuclei called band of stability

Half Life – the time required for one-half the sample to decay Can be very short or very long

SymbolElementRadiationHalf-Life Decay Product U-238Uranium-238alpha 4,460,000,00 0 years Th-234 Thorium-234beta24.1 daysPa-234 Protactinium -234 beta1.17 minutesU-234 Uranium-234alpha247,000 yearsTh-230 Thorium-230alpha80,000 yearsRa-226 Radium-226alpha1,602 yearsRn-222 Radon-222alpha3.82 daysPo-218 Polonium- 218 alpha3.05 minutesPb-214 Lead-214beta27 minutesBi-214 Bismuth-214beta19.7 minutesPo-214 Polonium-214alpha 1 microsecond Pb-210 Lead-210beta22.3 yearsBi-210 Bismuth-210beta5.01 daysPo-210 Polonium- 210 alpha138.4 daysPb-206 Lead-206nonestable(none)

Alpha Radiation (Helium Atom) Low penetrating power Paper shielding Beta Radiation (Electron) Moderate penetrating power Metal foil shielding Gamma Radiation (Pure energy) Very high penetrating power Lead/concrete shielding

Transmutation – conversion from one element to another through a nuclear reaction Only occur by radioactive decay Only when nucleus bombarded with a particle Emissions – given off Alpha Emission, Beta Emission, Positron Emission Positron = beta particle with a positive charge Captures – taken in Electron Capture