* Atom is the smallest particle of an element- All 117 elements has atoms * Bohr model: - Planetary model (see Figure 1 below)
1. Sun (proton & neutron= nucleus)
2. Planets (electrons)
3. Orbit (shell)
Figure 1: Bohr model
* Each type of atoms has a certain number of electrons and protons that differentiate it from the atoms of other elements Example: 1 proton 1 electron= Hydrogen (1 type elements)
2 proton, 2 neutron, 2 electron= Helium (other types elements) * There are many types of elements and it depends on the number of proton, neutron, and electron.
* Elements are arranged in the periodic table (Jadual berkala) * Atomic number =Number of proton in Nucleus. (No of proton=No of electrons) Example: 1 proton, 1 electron = Hydrogen (Atomic Number 1) in neutral (neutral) state (pada keadaan asal) 2 proton, 2 neutron, 2 electron= Helium (Atomic Number 2) in normal (neutral) state (pada keadaan asal)
* All atoms of an element have the same number of electrons as protons * The Positive charge (Protons +ve) cancels the negative charges (Electron -ve).
ELECTRON SHELLS (Petala) and ORBITS
* Electron orbits the nucleus (proton & neutron) of an atom at certain distance. ( Elekton berpusing sekeliling nucleus dalam jarak tertentu)
Figure 2: Electrons energy increases as it is father from the nukleus * Elektrons near the nucleus have less energy than those in more distant orbits (Shell). * Based on Figure 2 above. The values of each electrons energy are Label as E. Notice as the electrons distance from the nucleas, its energy level increases (J). * In an atom, the orbits are grouped into energy band knows as SHELLs. * Atoms has fixed number of shells. Each shell has a fixed maximum number of electrons at a certain energy level. * The differences in energy levels within a shell are much smaller than the diffrence in energy between shells. * The shells (n) are in numbers n=1,2,3,4,5….n..
* Shell no 1 (n=1) is the nearest to the nucleus and valence shell is the farthers. * The number of electrons in each shell.
* The maximum number of electrons (Ne) that can exist in each stage of shell of an atom is Ne=2n2
n=shell no, i.e. n=1,2,3,4,…n
Number of electrons in shell 1, n=1, Ne=2(1)2=2 Number of electrons in shell 2, n=2, Ne=2(2)2=8
Number of electrons in shell 3, n=3, Ne=2(3)2=18
Number of electrons in shell 4, n=4, Ne=2(4)2=32
* The atomic number, Z, should not be confused with the mass number, A, which is the total number of protons and neutrons in the nucleus of an atom. * The number of neutrons, N, is known as the neutron number of the atom; thus, A = Z + N. * Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes), the atomic mass of an atom is roughly equal to A.
Figure 3: Energy Band
* Based on above Figure 3, it shows the Energy band concept, the 1st shell with one energy level and the 2nd shell with 2 energy level. Aditional shells may exist in other types of atoms, depending on the elements.
* Outermost shell is knows as valence shell and electrons in this shell are called velence electrons.
* Electrons that are in valence shell from the nucleus have higher energy but are less tightly bond to the atom than those closer to the nucleus as shown in Figure 4. Valence Shell
Less bonded because electron are the farthest from the nucleus, less pull from the nucleus
Figure 4: Electron which are the farthest is not tightly bonded with the nucleus
* This is because the force of attraction (tarikan diantara)positively charged protons and negatively charged electrons decreases with increasing distance from nucleus.
* Electrons with the highest energy level exist in...