Chemistry: Everything about Atoms

Chemistry: Everything about Atoms

1. The Structure of an Atom

   • atoms form everything in our universe.
     • They consist of three particles: the proton, neutron and electron.
       • electrons have a -1 charge.
         • electrons 'circle' around the nucleus of the atom in 'orbitals'.
       • protons have a +1 charge
         • Relative mass: 1
       • neutrons don't have a charge!
         • Relative mass: 1

2. Nuclear Symbols

   • you can work out the number of protons, neutrons and electrons from the nuclear symbol
   • mass number: the number of protons and neutrons in the atom's nucleus
   • atomic (proton) number: number of protons in the atom.
     • all atoms of the same element have the same proton number!

3. Atoms and Ions

   • neutral atoms (no charge) have the same electron and proton number.
   • the neutron number is just the mass number minus the atomic number, i.e. "the top minus the bottom" (Nuclear Symbols)
   • Ions
     • Ions have different number of protons and electrons.
     • Negative ions (e.g. Br-) have more electrons than protons.
     • Positive ions (e.g. Mg2+) have more protons than electrons.
     • Ions are easy to spot: they always have a plus or minus charge (+ or -) next to them! If the charge is a plus, it means an electron has been lost, e.g. Mg2+ means that the Magnesium ion has lost two electrons. If there is a minus sign, it means electrons have been gained. For example, 3- means 3 electrons have been lost!

4. Isotopes

   • Isotopes of an element are atoms with the same proton number, but different neutron number.
     • basically atoms with the same number of protons but different neutron number are isotopes.
     • different isotopes of the same element react (chemically) the same way

5. Atomic Theory

   • An explanation supported by many experiments; is still subject to new experimental data, can be modified, and is considered successful if it can be used to make predictions that are true
   • Dalton’s Atomic Theory
     • Thanks to advancements in science since Democritus’s day, Dalton was able to perform experiments that allowed him to refine and support his hypotheses. He studied numerous chemical reactions, making care- ful observations and measurements along the way. He was able to deter- mine the mass ratios of the elements involved in those reactions. The results of his research are known as Dalton’s atomic theory, which he proposed in 1803.
   • Dmitri Mendeleev
     • Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.
   • Schrodinger
     • Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom

6. Coulombic Attraction

   • Attraction that occurs between oppositley charge particles
     • Attraction between protons (+) in the nucleus to the electrons (-) surrounding the nucleus
   • Effective Nuclear Charge
     • Net positive charge 'felt' by the VALENCE electrons

7. Ionization Energy

   • Its the energy required to completely remove an electron from a gaseous atom or ion

8. Electronegativity

   • Property of an atom which increases with is tendency to attract the electrons of a bond
   • It is a measure of an atom's ability to attract electrons to form a chemical bond

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