can some one explain why the size of atoms increses as you move down a group in the periodic table and decrese as you moce dsown accross a period
209152
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.
418003
Atomic radius shows a trend which is decreasing as one moves from left to right and top to bottom along the periodic table.
2089
Hello Partheek. \n    Well it is natural to prefer stability. Like look at yourself. Would you like to be runnung here are there in search of work or would you prefer a good sastisfying job. We all like to be stable in life. So is true with the atoms. They too like to rach a stabler configuration. Hence they try to attain it. Well you know even when you go to sleep, of you think deeper, you sleep because you ned rest. Rest from movement and motion. Hence you grow stabler. See it is all connected. So you dont sleep to attaion the octet but you do sleep to attain stability!!
89726
Danmergury is totally right.\n\nHere's a link to the periodic table:\nhttp://www.webelements.com/\nSo that you can see what he's talking about with the different groups having different charges.\n\nYou can think of it like this: \nThe atomic number (like 4 for Be) is the number of protons, as well as the number of electrons. So Be has 4 electrons. So you can think of adding a proton and electron each time you go to the next element on the periodic table.\n\nBut let's focus on the electrons. To count them up in Be, you start at H, then go over to He. Every time you reach the end of a row in the periodic table you have completed a shell. This makes elements stable and happy. But we have to keep going to get to Be. So you add another electron as you go past Li and finally you get to Be with 4 electrons.\n\nSo -- If you look at that periodic table, Be has those 2 extra blue electrons that are keeping it from being like He, which is a happy element. That last row is sometimes called the Noble Gases. All the other elements wish they were as cool as the noble gases. So Be is gonna get rid of it's 2 extra electrons to try to be like He.\n\nDoes that kinda make sense?\n\nIn a similar way, S is only 2 electrons away from being like Ar. So S tries to find 2 electrons that it can steal from another element so that it can be like Ar.\n\nGood luck with your classes!
157027
Atomic radii decrease as one moves from left to right across a period and while moving up a group. The atomic radius is the distance between the nucleus and the valence electrons.\n\nElectron affinity, ionization energy, and electronegativity increase as one moves from left to right across a period and while moving up a group. \n\nElectron affinity is the ease with which an atom can accept an electron. The halogens (F, Cl, I, etc.) have the highest electron affinity, with F having the highest of all elements. The alkaline metals (Li, Na, K, etc.) have the lowest electron affinity, with Fr having the lowest of all elements.\n\nIonization energy is the energy needed to remove an electron from an atom. All atoms want to form a stable octet. Since alkaline metals only have one valence electron, it takes very little energy to remove an electron from them. In contrast, it takes a lot of energy to remove an electron from a halogen.\n\nElectronegativity is the strength of the attraction an atom has for an electron in a chemical bond. Halogens are the most electronegative, while the alkaline earths are the least. The electronegativity of two elements can inform you of what type of chemical bond they will form. If Na (low EN) and Cl (high EN) form a bond, Cl will rip the lone valence electron away from Na, forming an ionic bond. If C and O form a bond, the atoms will share electrons because their EN's are very close. Since O is more EN, it will have a slight negative charge, and the bond will be a polar covalent bond. If C and C form a bond, both have the same EN, and they will form a non polar covalent bond.
465980
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.
415803
If you think of the radii of the orbitals as being rungs in a ladder, the rungs get closer together as you go up the ladder (get further away from the nucleus of the atom).  The reason why they get closer together is simply as there are more stable standing wave formations for electron orbitals the further you get away from the nucleus.\n\nThis is why the size of the atoms slow down in their increasing as you go down any group, not just the alkali metals.
78115
the numbers are on some better periodic tables\nthey fall out of valence and periodicity\nbut I must admit there is a lot to it
531836
all aelements in the same group have same number of electrons in their outermost orbit. but as you go down the group the number of orbits go on increasing and so there will be change in properties like ionization energy, electron affinity etc.\n\nnoble gases have got 8 electrons in their outermost shell or orbit. as we know that 8 electrons are required to complete octet, they have already a stable octet, so they don't require to loose or gain electrons to become stable as they are already stable, so they are unreactive\n\nthe period in which the element is present represent the number of shell of that element. for eg Mg has atomic number 12 so it will have 3 orbits or shell so it will appear in period III. all elements in same period will have same outermost orbit but number of electrons will go on increasing as their atomic number goes on increasing.\n\ni hope this will help you out
478144
A) Valence Electrons\n\nI believe b, c and d show the results of the grouping not the reason they're grouped that way to start out with...\n \nb... No... The atom size increases instead of decreases\nc... No...\nc... No...  \nversa...
546582
This is an answer I gave a few weeks ago. It helped me to get from failing Chemistry to University....maybe it will help you to understand the periodic table as well.\n\nMy Chemistry teacher taught me a great story which helped me learn the elements, which groups they were in, which periods, how many electrons they had etc and resulted in me going from a grade F to B. Every kid should learn this.\n\nHorrible Hairy Little Begger Boys Catch Newts On Friday Near Naples, Magnificent Albert Sits Planning Some Clever Arrangement Keeping Calm.\n\nOk, looks crazy until you break it down;\n\nH He Li Be B C N O F Ne Na, Mg Al Si P S CL Ar K Ca\n\nThen put it into the table\n\nH\nHe\nLi Be B C N O F Ne\nNa Mg Al Si P S Cl Ar \nK Ca\n\nYou will need to line them up because Yahoo has left align, but the trick is the story. \n\nThe groups 1-8 tell you how many electrons are in the outer shell, the periods tell you how many shells etc\n\nHope this helps!
228411
This is an subject area where vocabulary is vital for clear understanding, to a degree I am not capable of, however the stuff that you ask about are so small that the only way to attempt to prove their existence is through mathematical formulae based on what we suspect to be true. Our lack of understanding on this subject, which is still very voung, means the answers available are sketchy at best compared to our understanding of molecular structure or atomic structure.\nWhat is known so far can be found in places like the noetic sciences knowledge centre, or wikipedia.
354788
B: Some mass is converted into energy in order to split the unstable nucleus into two, smaller, stable ones.\n\nC: Their nuclei are too big to remain in one lump of mass. Particles (alpha, beta, gamma, etc) start shooting off in all directions, to bring the nucleus down to a smaler size. It's all about the smaller size.\nAlso, no atom can have more than one nuclues, because then it would be two atoms. More or less elctrons make an atom into a charged ion, not an isotope. Neutrons are what make isotopes.
488796
Because they have smaller masses and can move quicker.  Because they are tiny there are less collisions with other atoms
299924
the answer is a, the number of outer shell electrons it can gain or lose.\n\nthia is because that outer electrons are the ones the define the atom in terms of bonding. \nmass nubmer and atomic number dont matter much [as lower level chemistry] for bonds. we know that the number of molecules it can form is infinite, and inner shells dont matter, leaving us wiht (A), the only right answer
473100
All three of these ions have the same number of electrons, they are "isoelectronic."  The size of the ions thus depends on the number of protons in the nucleus.  As we move to the right across a row on the periodic table, the number of protons in the nucleus, and thus the nuclear charge, increases.  This increase in nuclear charge pulls the electrons in tighter, thus reducing the size of the ions.  Na+ > Mg2+ > Al3+
647455
Look on a periodic table.\n\nIt should be listed below the atomic number as a decimal value.  The mass number is an average mass (in atomic mass units) of an element, based on different isotopes.  It equals the number of protons + the number of neutrons in the nucleus.