How do you know if an atom is bigger?

Answer 1

The number of full, or partially filled, electron shells determines the size of an atom. The size of the outermost shell depends on how many protons in the nucleus can 'see' that electron shell to pull it inwards. The larger the number of 'unshielded' protons, the stronger the pull.

When the number of electrons increases the number of filled, or partially filled, shells can also increase. If we move down groups the size of atoms increases, because more shells are filled. If we move across periods, the atomic size decreases, because there is a larger number of 'unshielded protons' on the nucleus to draw the shell inwards.

The definition of atomic size is half the separation of two atoms of the same element. This will depend on how closely and strongly the atoms are bonded.

Radii are metallic radii when it is a metallic bond; covalent radii when the bond is covalent; and when no strong bond is present, and the atoms are 'just touching', it is called a Van der Walls radii. On the whole, metallic radii are smaller than covalent, which are smaller than Van der Walls.

Ionic radii are more complex, as metallic ions have a smaller ionic radius than their related metallic atoms, as they have lost electrons to form their ions. Non-metallic ions are larger than their related atom, as they tend be negative ions, formed by the addition of electrons.

Estimates and measurements of atomic radii can be approached from considerations of volume, by assuming the atoms are spherical and closely packed, in a solid or a cold liquid sample. This allows the a good estimate of how much of that sample volume is a 'void', and how much is an 'atomic' volume. From the volume of a sample, the sample mass, and the Atomic Mass, the number of atoms in the sample can be calculated, and so the volume of each atom. The radius can be worked out from this using the formula for the volume of a sphere.

Other more accurate methods exist, including X-ray crystalograhy, which uses the diffraction pattern from a crystal to determine the distances between atoms.

Answer 2

Easy way: if there are 2 elements in the same row then the one farthest to the right will be biggest, if there are 2 elements in the same column then the one farthest down is the biggest.

Answer 3

because hydrogen atom have 2 atom they can not exist in single form

Answer 4

by knowing its atomic number.