why does the size of atoms increses as you move down a group in the periodic table?
462594
As you go down, the electrons occupy energy levels whose energy is greater. That is, they are farther away from the nucleus. For example an element in period 6 has its outtermost electrons in the n=6 energy level. These electrons have a greater potential energy than those in the n=2 level because they are farther away from the nucleus. This is similar to an object that is higher up: It has a greater gravitational potential energy. The size of the atom increases because as more electrons are present in an atom, the more energy levels they fill. The outtermost occupied energy level of an atom is what determines size.
123587
Periodic Table is in order of increasing atomic no. so\n\n1st Step: find the placement of the element, in the present case it is on third place so no. of protons is three.\n\n2nd Step: In the Periodic Table, number of electron is always equal to number of protons so far three protons of Lithium there will be three electrons.\n\n3rd Step: Periodic Table also give atomic weights of the elements. Simply atomic weight is equal to sum of number of protons and nutroms.\n\n4th Step: Note the atomic weight of the element. Most of the elements in Periodic Table show atomic weights in fractions. In the case of Lithium it is 6.9 \n\n5th Step: Convert the fractional figure into nearest whole number. In case of Lithium it is 7\nNote:In the Periodic Table atomic weight is average of all isotopes (different atomic weights of same element). The nearest whole number refers to the most abundent  or the common atom (Isotop).\n\n6th Step: Subtract atomic number (protons) from atomic weight (neutron=proton), the difference is number of neutrons. In Lithium 7-3=4 so there are 4 neutrons
253224
Larger surface area for the electrons to spread over.  In other words, the reason elements in the same family decrease in electronegativity downward is because the atoms bet larger.  For instance, Fl, the most electronegative element, is many times smaller than Cl, then Br, I.  I think you get the point.
948794
protons is the atomic number\nvalence electrons corresponds to this:\nGroup 1 (I) (alkali metals) :1\nGroup 2 (II) (alkaline earth metals) :2\nGroups 3-12 (transition metals) :1 or 2\nGroup 13 (III) (boron group) :3\nGroup 14 (IV) (carbon group) :4\nGroup 15 (V) (nitrogen group) :5\nGroup 17 (VII) (halogens) :7\nGroup 18 (VIII or 0) (noble gases) :8\n\n\nEvery element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons. It goes down the periodic table like that. At this time, the maximum number of electron orbitals or electron shells for any element is seven.
47846
Look up the atomic mass (sometimes called atomic weight) on the periodic table, and subtract the atomic number from it.  The atomic mass is (practically) equal to the total number of protons and neutrons, and the atomic number is equal to the number of protons.  When you subtract atomic number from atomic mass your subtracting the number of protons from the total number of protons and neutrons, which leaves you with just neutrons.
252404
An element is reactive because it is unstable.By reacting with other substances it tries to become stable.\nin case of metals or as u say positively charged elements,say,Li,Na,K...the atomic size is increasing on going down.As the size increases the the nuclear pull for the valence shell decreases,thereby making it easier to lose electrons.Thus,K easily loses electrons as compared to Na or Li and is therefore more reactive.\nin case of negatively charged atoms or non metals,the atomic size is again increasing for eg in case of F,Cl,Br..\nbut the case is opposite here.\nthe atom has to gain one electron in order to become stable.\nthe smaller the atom the more is the nuclear pull for the incoming electron and more readily it is accepted.\nthus in this case,reactivity decreases down the group.
495461
Atomic radius (or size) increases as you go down and to the left on the periodic table.  Therefore, out of these, the largest would be K.
756517
Atoms have mass which can sometimes have volume and there are about 6.022x10^23 particles in a mole of an element. A mole of an element is the atomic mass in grams. Now, you can use all this and do some further research on the Internet and in books to write a nonfiction book on atoms and how the periodic table of the elements is set up.
1026057
The positive force of the protons is increasing as they increase they pull stronger on the electrons to make the atom smaller. This only happens across a period in the periodic table.
845987
K, Na, Li, Be ... its already arranged from largest to smallest atomic radius. \n\nFor Potassium, Sodium and Lithium, they belong to the same group, so size increases from top to bottom. Lithium being on the top of the other is the smallest. \n\nBeryllium is on the right of Lithium, so it has one proton extra than Lithium but the number of shell is the same so its nucleus pulls the outer electronic shell with more force, hence its atomic radius is even smaller than Lithium.
423557
Basically, from left to right in a period, the metallic character of the elements decreases and non-metallic character increases i.e. the elements lose the tendency to give off electrons and instead tend to accept or share electrons.\nGroupwise, the reactivity of elements generally increases down the group in order of increasing atomic number, except in group 7 where the most reactive element is at the top and least reactive at the bottom. \nI don't suppose there is any relationship as such - you can't say the reactivity increases in order of increasing atomic number; you can only compare the reactivity in terms of groups and periods; including exceptions like hydrogen, group 7 elements and lithium for instance (which undergoes some reactions that are not the characteristics of group 1).
451270
its how the electrons fit into the shells around the nucleus. at gcse there are 4 and they have the rule 2.8.8.18 so the first shell is filled first with two and then the second with 8 and so on.the number of electrons in the outer most shell used gives the atom its properties and its position on the periodic table
607033
The order of elements in the periodic table is determined by their atomic number, or number of protons (positively charged particles. The nucleus of the element is made up of protons and neutrons (neutral subatomic particles), and nearly all of the mass of the element resides here. \n\nElectrons "circle" the nucleus to even out the charge of the atom. The electrons organize themselves in layers, with a certain number of electrons in each layer. These layers are also referred to as the valence of the electron. The first layer has 2 electrons, the second and third have 8, the fourth has 18... These layers are what give the atom its volume.\n\nSince density is mass/volume, there isn't a linear relationship for density in each successive element, but the trend is density increases from left to right and top to bottom.
932777
ok. To tell which elements are more metallic then others, It depends on the left over valence electrons that are attracted to the positively charged cations in a metal. To tell which elements are more active then others it is towards the right of the periodic table. Noble gases are non-reactive. To tell which atoms are bigger then others remember going from top to bottom in a group, atomic size increases, going from left to right across a period, atomic size decreases.(there is a pattern to this). \nI think if there are more valence electrons, the stronger the metallic bond is.
536511
If you mean atomic radius, the atoms.  The ions will most likely have shed their outer electrons to form the ion, such as Ca +2, while the atoms keep that outer shell, which increases the radius.\n\ndkrgrand:  That's the whole point.  The size of Ca (the metal) is bigger than the size of Ca+2 (the ion) because of the missing shell.  This is what was asked.
23478
Could you be a little more specific?  Are you asking how the atomic weights in the periodic table derived?
866693
It has to do with periodic table trends. In Metals the melting point generally decreases as you go down a group. Non-metals the the melting point generally increases as you go down a group.\nNa is a Metal, K is a Metal, therefore Na possesses a higher metling point because it is above K on the group.