This is due to the fact that while they are attracted to the positively charged nucleus, they are repelled by the negatively charged electrons in lower energy levels. Remember that like charges will repel. This means that for every additional energy level, there are more and more electrons in lower energy levels that will repel the electrons in the highest energy level of an atom.
This means that the outer electrons experience an attraction to the positive nucleus that is much weaker than electrons in lower energy levels. This is why elements that are lower in a group will lose electrons much more easily than elements that are higher in the group. You might find this video helpful in understanding trends of the periodic table. Does the electron shielding increase or decrease as you go down a group for atomic radii? Oct 25, How is it called the effect of electronegative atoms on their neighbours?
What is the pi -bond effect? What happens if the electron density around a nucleus is decreased? How can I read in the NMR spectrum when increasing chemical shift? See all questions in Electronegativity and Shielding. Impact of this question views around the world. You can reuse this answer Creative Commons License. Electron shielding describes the ability of an atom's inner electrons to shield its positively-charged nucleus from its valence electrons.
When moving to the right of a period, the number of electrons increases and the strength of shielding increases. As a result, it is easier for valence shell electrons to ionize, and thus the ionization energy decreases down a group.
Electron shielding is also known as screening. Some elements have several ionization energies; these varying energies are referred to as the first ionization energy, the second ionization energy, third ionization energy, etc. The first ionization energy is the energy requiredto remove the outermost, or highest, energy electron, the second ionization energy is the energy required to remove any subsequent high-energy electron from a gaseous cation, etc.
Below are the chemical equations describing the first and second ionization energies:. Generally, any subsequent ionization energies 2nd, 3rd, etc. Ionization energies decrease as atomic radii increase. The relationship is given by the following equation:.
As the name suggests, electron affinity is the ability of an atom to accept an electron. Unlike electronegativity, electron affinity is a quantitative measurement of the energy change that occurs when an electron is added to a neutral gas atom. The more negative the electron affinity value, the higher an atom's affinity for electrons. Electron affinity generally decreases down a group of elements because each atom is larger than the atom above it this is the atomic radius trend, discussed below.
This means that an added electron is further away from the atom's nucleus compared with its position in the smaller atom. With a larger distance between the negatively-charged electron and the positively-charged nucleus, the force of attraction is relatively weaker. Therefore, electron affinity decreases. Moving from left to right across a period, atoms become smaller as the forces of attraction become stronger.
This causes the electron to move closer to the nucleus, thus increasing the electron affinity from left to right across a period. The atomic radius is one-half the distance between the nuclei of two atoms just like a radius is half the diameter of a circle. However, this idea is complicated by the fact that not all atoms are normally bound together in the same way.
Some are bound by covalent bonds in molecules, some are attracted to each other in ionic crystals, and others are held in metallic crystals. Nevertheless, it is possible for a vast majority of elements to form covalent molecules in which two like atoms are held together by a single covalent bond.
The covalent radii of these molecules are often referred to as atomic radii. This distance is measured in picometers. Atomic radius patterns are observed throughout the periodic table. Atomic size gradually decreases from left to right across a period of elements. This is because, within a period or family of elements, all electrons are added to the same shell.
However, at the same time, protons are being added to the nucleus, making it more positively charged. The effect of increasing proton number is greater than that of the increasing electron number; therefore, there is a greater nuclear attraction. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. The valence electrons are held closer towards the nucleus of the atom.
As a result, the atomic radius decreases. D own a group, atomic radius increases. The valence electrons occupy higher levels due to the increasing quantum number n. Electron shielding prevents these outer electrons from being attracted to the nucleus; thus, they are loosely held, and the resulting atomic radius is large.
The melting points is the amount of energy required to break a bond s to change the solid phase of a substance to a liquid. Generally, the stronger the bond between the atoms of an element, the more energy required to break that bond.
Because temperature is directly proportional to energy, a high bond dissociation energy correlates to a high temperature. Melting points are varied and do not generally form a distinguishable trend across the periodic table. The metallic character of an element can be defined as how readily an atom can lose an electron. From right to left across a period, metallic character increases because the attraction between valence electron and the nucleus is weaker, enabling an easier loss of electrons.
Metallic character increases as you move down a group because the atomic size is increasing. When the atomic size increases, the outer shells are farther away. The principal quantum number increases and average electron density moves farther from nucleus.
The electrons of the valence shell have less attraction to the nucleus and, as a result, can lose electrons more readily. This causes an increase in metallic character. Another easier way to remember the trend of metallic character is that moving left and down toward the bottom-left corner of the periodic table, metallic character increases toward Groups 1 and 2, or the alkali and alkaline earth metal groups. Likewise, moving up and to the right to the upper-right corner of the periodic table, metallic character decreases because you are passing by to the right side of the staircase, which indicate the nonmetals.
These include the Group 8, the noble gases , and other common gases such as oxygen and nitrogen. Based on the periodic trends for ionization energy, which element has the highest ionization energy? Answer: C. Helium He Explanation: Helium He has the highest ionization energy because, like other noble gases, helium's valence shell is full.
Therefore, helium is stable and does not readily lose or gain electrons. Answer: A.
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