Essay on Chapter 1 notes for grade 11 chemistry

Submitted By rhiannalad
Words: 658
Pages: 3

Periodic Table Development:
• 18th century, discovered elements each had their own mass
• Mendeleev organised the periodic table in terms of increasing atomic mass, (protons, neutrons and electrons were not yet discovered)
• He left spaces for elements not yet discovered
• Henry Moseley: he discovered that when he bombarded atoms with electrons, the wavelengths of the x-rays emitted by the atoms were related by the integer Z (the atomic number.)Rutherford realized that this was the number of the protons and electrons.

• Isotope has a different number of neutrons, but the same number of protons.

• Radioisotopes: The isotopes that is radioactive.

• Z: the atomic number, a: the mass number (the total number of protons and neutrons. Z- lower left, A- upper left

• Neutrons hold the nucleus together

• Now alkaline metals, alkaline earth metals, halogens and noble gases

• Nails Bohr discovered the energy levels around the nucleus. Energy levels: 2, 8, 18, 32. Formula for the number of electrons is 2n (squared.) the v valence shell cannot contain more than 8 electrons.

• When elements in a group react, they will most likely react in the same way, because they have the same number of electrons in their valence shell. The intensity of the reaction changes as you go down a group. Metals: reactivity increases down the group non-metals: reactivity decreases as you go down a group. The most reactive elements have either 1 or 7 valence electrons.

• In the universe, approx. 92% of all atoms are hydrogen and 7% are helium. On earth, 97% is nitrogen, and 27% is oxygen.

• Atomic Radius: As you go left to right across a period, the atomic radius decreases, because the number of protons increases, but the number of shells is the same. The number of electrons has also increased. The nuclear attraction with the increased number of protons pulls everything in and makes it more compact.
• As you go down a group, the atomic radius increases because there are a larger number of shells and electrons. There is also less of a nuclear pull and more of an electron repel.
• Ionization Energy is the amount of energy needed to remove an electron from a gaseous atom.
• This increases as you go left to right because there is a stronger attraction between the electrons and the nucleus.
• As you go down a group, the I.E because the electrons are further from the nucleus and there is less of an attraction.
• Electron Affinity: the amount of energy released when an electron is added to a gaseous atom. The E.A. (E) increases as you go L to R across a group. This is because this is more likely to occur to the right of the periodic