why atomic size decreases in a period of periodic table?

Answer 1

As you move from left to right in a period of a periodic table, the number of shells does not change, but, the number of electrons and protons increases. The increase in number of electrons (negatively charged particles) and protons (positively charged particles) increases the Coulomb's force of attraction between them. Strong coulombic force pull these oppositely charged particles closer resulting in a decrease in the atomic size.

Answer 2

The atomic size is defined by the distance between the valence electrons and the nucleus. The further away the valence electrons (the outermost electrons in an atom) are from the nucleus, the larger the atomic size is.

Now, as you go down a group (vertical), the amount of valence shells increase (with more electrons) which affect the pull of the protons of the nucleus and the electrons. (They are opposite charges, and opposite charges attract.) The pull is decreased because of these valence shells. This is called shielding.

Now, as you go across a row (horizontal), the atomic size decreases as you say (though there are some exceptions due to some electron configurations, such as the infamous palladium's octet stability). The more valence electrons on the outermost valence shell, the greater the pull of the electrons towards the nucleus. I will use the noble gases (Group 18 elements, or the last group on the table) as an example. All noble gases have octet stability (they have 8 valence electrons), and the atomic size is therefore smaller (as explained before by the pull of the electrons and the protons). However, the first group has only 1 electron, so the pull is not as strong, thus explaining the atomic size.

To summarize, if my repetition hasn't payed off enough, the pull of the electrons towards the protons in the nucleus and the valence shells (if you're going down a group) is what affects the atomic size of an atom.

Answer 3

Each atom has a nucleus inside and electrons zooming around outside the nucleus. It should seem reasonable that the size of an atom depends on how far away its outermost (valence) electrons are from the nucleus. If they are very close to the nucleus, the atom will be very small. If they are far away, the atom will be quite a bit larger. So the atomic size is determined by how much space the electrons take up.

Measuring the size of atoms is, in some ways, like measuring the size of cotton balls or automobile tires. The value you get depends on the conditions under which they are measured. A "free" cotton ball has a different size than when it is in the package. The radius of the tire is different when measured to the top of the tire than when measured to the bottom of the tire resting on the ground. Different values for the sizes of atoms are obtained depending on both the method used and the conditions in which the atoms find itself - free or bonded to other atoms.

In a family--like from hydrogen to lithium to sodium on down--the atomic size increases. As you go down a group, the size increases. As you go across a period, as from lithium to neon, notice that the size decreases.

The nuclear charge and the shielding electrons combine to make the effective nuclear charge. That is a very important factor when you are comparing elements in a period. As you go across a period, the nuclear charge increases and the number of energy levels stays the same. Consequently, the number of shielding electrons stays the same and the effective nuclear charge increases. As the effective nuclear charge increases, it pulls the electrons in closer and closer to the nucleus. So as you go across a period, the increase in the nuclear charge causes a decrease in the atomic size because the electrons in the valence energy level are pulled in closer and closer.

Answer 4

An atom consist of a nucleus in the centre & is covered with electrons .As we move across a period the no of electrons increases because of which the attraction power of nucleus on the electrons increases (+ve & -ve charge attracts each other) thus the nucleus pulls elecrons towards it & the atomic size decreases.

Answer 5

Remember that the nuclear charge and the shielding electrons combine to make the effective nuclear charge. That is a very important factor when you are comparing elements in a period. As you go across a period, the nuclear charge increases and the number of energy levels stays the same. Consequently, the number of shielding electrons stays the same and the effective nuclear charge increases. As the effective nuclear charge increases, it pulls the electrons in closer and closer to the nucleus. So as you go across a period, the increase in the nuclear charge causes a decrease in the atomic size because the electrons in the valence energy level are pulled in closer and closer.

Answer 6

because in periods atomic number goes on increasing but the electrons are being added in the same shell therefore attraction between nucleus and outermost electrons increases hence size decreases

Answer 7

as we move in the period the electrons r concentrating in the same orbit (the +ve charge atrracts the -ve) which results in the increase of net nuclear effect increases.the valence shell is attracted so the size decreases

Answer 8

as the electrons and protons in the element's atom increase , the magnetic force between the +(of protons) and the -(of electrons) also increase => they came closer to each others=> the size decrease

Answer 9

when you move across the period ,the extra electron is added in the same outer shell (ie,valence electrons increase).
so as no of electrons in outer shell increases the attraction between the nucleus and these electrons increases resulting in reduction(shrinking) of the size of atom as the outer orbital is attracted inwards.

Answer 10

i think it is bcoz the stability of atom increases, and so it attracts the electrons closer to the nucleus, you see nucleus has positive charge n hence it attracts the electron orbits towards itself. this in turn reduces the size of the atom. i hope this answer is comprehensive