ALL TOPICS

Dalton’s Model

  • Elements are made of Atoms

  • Atoms of an element are the same

  • Compounds are formed from combinations of atoms

Rutherford Experiment

  • Bombarbed gold foil with alpha particles. Showed atoms were mostly empty space with small, dense positively charged nucleus

Bohr Model

  • Small, Dense, positively charged nucleus surrounded by electrons in circular orbits

Wave Mechanical Model

  • Small dense, nucleus

  • Positively charged

  • Surrounded by electrons moving in electron cloud

  • “Orbitals” are areas where an electron with a certain amount of energy is most likely to be found”

  • The # of protons are equal the # of electrons

  • Each electron in an atom has its own distinct amount of energy

  • Electrons fill in energy levels and orbitals starting with the one that requires the least energy, valence electrons require the most energy

  • When the electron gains a specific amount of energy, it moves to a higher orbital and is in the ‘excited state’

  • When an electron returns from a higher energy state to a lower energy state, it emits a specific amount of energy, usually in the form of light

The stabilty of an isotope depends on the ratio of protons to neutrons in the nucleus

  • The nuclei will spontaneously decay, emitting radiation

  • Stable isotopes have a 1:1 proton to neutron ratio

  • All elements 83+ are radioactive

A change in the nucleus of an atom changes it to a new type of atom is called transmutation

  • Artifical transmussion requires the bombardment of a nucleus by high energy particles

Nuclear reactions include natural and artifical decay, nuclear fission and nuclear fusion

  • Nuclear fission occurs when the nucleus of an atom is. split. This can be caused by shooting the nucleas with an electron

  • Nuclear fusion combines two light nuclei to form heavier nulcei.

  • Nuclear fusion requires high tempatures

  • The energy released from nuclear reactions is much greater than the released from chemical reactions

  • Breaking a chemical bond is a endothermic process

  • forming a chemical bond is an exothermic process

  • compounds have less potential energy than the individual atoms they are formed from

Compounds can differenciate by their chemical and physical properties

  • Ionic substances have high melting and boiling points, form crystals, dissolve in water and conduct electricity in solutions as a liquid

  • Covalent or molecular substances have lower melting and boiling points, do not conduct electricity

  • Polar substances are dissolved only by another polar substance. Non-Polar substances are dissolved only by other non-polar substances

Chemical bonds are formed when valence electrons

  • Ionic- Transferred from one to another

  • Covalent- Shared between atoms

  • Metallic- Mobile in a free moving ‘sea’ of electrons

Polarity of a molecule can be determined by its shape and the distribution of the charge

  • Polar molecules must have polar bonds

  • Polar molecules are asymmetrical

  • Non Polar molecules are symmeterical and or have no polar bonds

  • Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond. These values are based on an arbitrary scale

The electronegativity difference between two bonded atoms can determine the type of bond and its polarity

  • 0.0-0.4- Non polar covalent

  • 0.4-1.7 Polar covalent

  • 1.7+ Ionic