MRCHEM

Explain how/why a metals reactivity increases going down a group and decrease going across a period 3

As you go across a period, the nuclear charge will increase; the number of energy levels will stay the same, so there is a stronger and stronger attraction for the electrons. The electrons are being held more tightly as you go across a period. It becomes more and more difficult to lose electrons and consequently the reactivity of the metals decreases as you go from left to right across the periodic table. Atomic number increases from top to bottom in the group. Hence atomic radii go on increasing, ionisation enthalpy decreases ,electronegativity decreases. Due to this metallic characters increases and nonmetallic characters decreases from top to bottom in the group.

Explain what happens inside an atom

Atomic electrons spread out into cloud-like wave shapes called "orbitals". The various orbitals of atoms all overlap in space. Therefore, when an electron transitions from one atomic energy level to another energy level, it does not really go anywhere. It just changes shape. The orbital shapes with more fluctuations (with more highs, lows, and bends to its shape) contain more energy. In other words, when an electron transitions to a lower atomic energy level, its wave shape changes to have less fluctuations in it. An electron disappears from the orbit in which it is located and reappears in its new location without ever appearing any place in between. This process is called a quantum leap or quantum jump, and it has no analog in the macroscopic world. Because different orbits have different energies, whenever a quantum leap occurs, the energy possessed by the electron will be different after the jump. For example, if an electron jumps from a higher to a lower energy level, the lost energy will have to go somewhere and in fact will be emitted by the atom in a bundle of electromagnetic radiation. This bundle is known as a photon, and this emission of photons with a change of energy levels is the process by which atoms emit light. In the same way, if energy is added to an atom, an electron can use that energy to make a quantum leap from a lower to a higher orbit. This energy can be supplied in many ways. One common way is for the atom to absorb a photon of just the right frequency. For example, when white light is shone on an atom, it selectively absorbs those frequencies corresponding to the energy differences between allowed orbits. Electrons cannot choose any orbit they wish. They are restricted to orbits with only certain energies. Electrons can jump from one energy level to another, but they can never have orbits with energies other than the allowed energy levels.

Explain how/why a metals reactivity increases going down a group and decrease going across a period 1

Metals react by losing electrons because they have a low ionization energy, which makes it easier for them to lose electrons. In metals, reactivity decreases across periods (left to right) and increases down groups. Atomic number increases down groups and hence the number of electron subshells also increases. The electron subshells between the valence electrons and the nucleus have a 'shielding' effect, which reduces the attraction of the valence electrons to the nucleus.

Explain how/why a metals reactivity increases going down a group and decrease going across a period 2

The elements on the left side of the table (i.e. group 1 and 2) going down: These react by losing electrons and reactivity increases as you go down the group. This is because the increased number of electron shells results in more shielding and a greater distance between the outer electrons and the nucleus, which reduces the attraction of the outer electrons to the nucleus. This means that less energy is needed to remove the outer electrons, so they are more easily lost. The elements on the right side of the table (i.e. group 7 and 6—not the noble gases): These react by gaining electrons and reactivity decreases as you go down the group. Again, this is because of the increased number of electron shells going down groups; it means that there will be a greater shielding effect and a greater distance between the outer electrons and the nucleus. This time, though the result is that the incoming electrons are less attracted to the nucleus and so are less easily gained.

How will the wavelength and frequency be affected if an electron goes from n=5 to n=2 instead of n=3 to n=2?

The n = 1 state is known as the ground state, while higher n states are known as excited states. If the electron in the atom makes a transition from a higher state to a lower state, it is losing energy (in this case it is going from n = 5, a higher energy level, to n = 2, a lower energy level. To conserve energy, a photon with an energy equal to the energy difference between the states will be emitted by the atom. The smaller the energy the longer the wavelength. Since energy is decreasing because of the fact that the electron is going from a higher state of energy to a lower one, the wavelength will increase and the frequency will decrease (longer wavelength, lower frequency). Atoms can also absorb photons. If a photon with an energy equal to the energy difference between two levels is incident on an atom, the photon can be absorbed, raising the electron up to the higher level