What is the significance of an electronegativity difference of 1.7 between 2 atoms?
O A. It tells which atoms form positive ions and which atoms form
negative ions.
OB. It represents the boundary between what is considered to be an
ionic or a covalent bond.
C. It determines if the 2 atoms will react to form a molecule.
D. It identifies which metal atoms will join together to form metallic
bonds
Am

B. It represents the boundary between what is considered to be an  ionic or a covalent bond.

Electronegativity is the ability of atoms to attract electrons, especially in covalent bonds (sharing of electron pairs)

In a periodic system, electronegativity increases in a group, from bottom to top, and in a period from left to right.

From this difference in electronegativity, we can determine the ionic compound, polar or non-polar

Pauling determined the electronegativity scale (based on bond energies), between 0.7 - 4 (Fluorine has the highest number of electronegativities: 4)

Polar covalent compounds have a large electronegativity difference, while nonpolar compounds have a small electronegativity difference.

We can use the difference in electronegativity between the 2 bonded atoms to determine their polarity

Example

H = 2.1

O = 3.5

H₂O = 3.5-2.1 = 1.4 >> polar

= 3.5-3.5 = 0 >> non polar

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.

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.