U4: ATOMS & THE PERIODIC TABLE

• The Atom is ALWAYS neutral; there are the same number of protons as electrons. But, there are also some non-neutral atoms called Ions.
• The Mass Number is the biggest number and is written with an A. It's the number of protons+neutrons.
• The Atomic number is the smallest number and It's written with a Z, is the number of protons.
• Dalton's atom theory was the secon one (1804)second.

  He thought that all atoms of the same elements were identical and that atoms couldn't be created or destroyed. He didn't specify what was in the atom.
• Democritus' was the first theory, (400BC) he thought that atoms were indestructible, hand and incompressible. He didn't carry out any experiments to support his theory.
• Thompson's theory was the 3rd one, and the ONLY WRONG THEORY (1897).

  He thought that atoms consist of negatively charged electrons enclosed in a sphere of uniform positive charge. He didn't mention protons or electrons, and he said it was positive.
• Rutherford was the FATHER OF CHEMISTRY, it was the 4th theory, he thought that a high central mass concentrated in the nucleus, electrons circulated around it and most of it was empty space. He was wrong because he didn't explain the stability. He carried out the GOLD WALL EXPERIMENT.
• Bohr's theory was the 5th one (1913), he thought that electrons move in fixed orbits and not anywhere in between. Each shell has a fixed energy. He was wrong because he lacked of information on how atoms form chemical bonds.
• Modern theory establishes the concepts of atoms and how they compose matter. Adding info to Borh's.Atoms consist of negatively charged electrons around a central nuclear composed made of positively charged protons and neutrons.
• On the GOLD WALL EXPERIMENT carried by Rutherford, he put a gold wall (loses e-) and threw alpha particles (2 protons) into it. He found:

  • 65% Alpha particles repelled
  • 25% pass the wall and change direction because they are attracted to negative
  • 10% pass the wall on a straight line
• The Optec Rule stable atoms that have a complete outer shell.
• An Ion is an atom that loses or gains electrons to become stable, the only stable atoms on the periodic table are the Nobel Gasses (Group 8/0)
• Cations are Ions with a positive charge, they loose electrons.
• Anions are atoms with a negative charge. they gain electrons.
• Ions are formed when atoms Lose or Gain electrons in order to have a Full Outer Valence Electron shell.
• Isotopes are atoms of the same element with different neutrons
• In Isotopes, Chemical properties (Protons, electrons) are the same, but Physical (Neutrons) no
• Johan Döbereiner's periodic table was the first one (1829), he carried out Döbereheiner's trials and arranged the atoms in groups of 3 elements that showed similar properties. It wasn't useful because he could only identify some
• Newlands Octave's periodic table was the 2nd one, he arranged the 56 elements in an increasing order of their atomic masses. He found that every 8 elements had properties similar to the 1st one. He only could arrange 17/56
• Dimitry Ivanovich is the FATHER OF THE PERIODIC TABLE, he examined the relationship between the atomic masses and the chemical & physical properties. He thought Atomic Mass was the most fundamental property in classifying elements. He also guessed the properties of some elements that hadn't been discovered yet.
• Mendeleveev´s law states that ​the physical and chemical properties of elements are a periodic function of their atomic masses (The theory was previous to the discover of noble gasses)
• The demerits of Mendeleev's periodic table where that there wasn't a fixed position for H (Hydrogen), and at some places, elements of higher Atomic Mass are placed before an element of lower mass.
• Henry Moseley's periodic table is the one that we use currently (1913). It disclaimed what was said by Mendeleev: The most important part is not the Atomic Mass, but the Atomic Number (Z)
• The modern periodic law (Actualized Mendeleev's law) states that the chemical and physical properties of elements are a periodic function of their Atomic Number (Z)
• The differences between Mendeleev's and the Modern Periodic Table are:

  • Elements: Mendeleev hadn't discovered all the elements, nowadays there are way more
  • Z: Mendeleev used the Atomic Mass, in the modern one the Atomic number (Z) is used instead
  • Nobel Gasses: Mendeleev's was previous to them, so they weren't included. In modern, they are included as Group 8/0
  • Gaps: In Mendeleev's there are gaps, but nowadays there aren't
• Periodicity refers to all the elements in a group that have similar properties
• Metalic Property is the ability to lose electrons. Group one is more metal because losing 1 electron is easier than losing 3
• Non-Metalic property is the ability to gain electrons. Group 7 is more non-metallic because it's easier to gain 1 than 3
• Reactivity Is the ability to react, the most reactive groups are 1 & 7. They go in pairs: Group 1 that loses one e- + Group 7 that needs 1 e-
• Li stands for Lithium, which is in the Group 1, Period 2
• Na stands for Sodium, which is in the Group 1, Period 3
• K stands for Potassium, which is in the Group 1, Period 4
• Rb stands for Rubidium, which is in the Group 1, Period 5
• Cs stands for Caesion, which is in the Group 1, Period 6
• Fr stands for Francium, which is in the Group 1, Period 7
• Be stands for Beryllium, which is in the Group 2, Period 2
• H stands for Hydrogen , which is in Group 1, Period 1
• Mg stands of Magnesium, which is in Group 2, Period 3
• Ca stands for Calcium, which is in Group 2, Period 4
• Sr stands for Strontium, which is in Group 2, Period 5