An unknown element has two isotopes. Isotope #1 has an atomic mass of 84.91 amu (72.16%) and isotope #2 has an atomic mass of 86.91 amu (27.84%). (a) What is the average atomic mass? Isotope #1: Х Isotope #2: Х (b) What is the element? amu

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

answer; talc and gypsum;

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

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