Why do non-metals not form Ionic bonds(Ti-C, Sc-P) and instead form covalent compounds?

Question

Is there something like, "sharing or gaining electrons gets harder", or is there something that lays hidden from common sight?

I am looking for a High-School Level Answer, pls something provide me with this answer..

Answer 1

Ionic bonds are created when there is big enough difference between attraction of valence electrons by respective atoms. The measure of this atraction ability is electronegativity.

In reality, there is no purely ionic nor purely covalent bond, with the exception for the same atoms, like $\ce{O2}$, $\ce{N2}$, $\ce{F2}$ etc. There is always some charge shift, but OTOH this charge is never fully transferred to either of atoms, while still bound by a mostly ionic bond.

Quoted from the Ionic bond link:

Purely ionic bonding cannot exist, as the proximity of the entities involved in the bonding allows some degree of sharing electron density between them. Therefore, all ionic bonding has some covalent character. Thus, bonding is considered ionic where the ionic character is greater than the covalent character. The larger the difference in electronegativity between the two types of atoms involved in the bonding, the more ionic (polar) it is. Bonds with partially ionic and partially covalent character are called polar covalent bonds. For example, Na–Cl and Mg–O interactions have a few percent covalency, while Si–O bonds are usually ~50% ionic and ~50% covalent. Pauling estimated that an electronegativity difference of 1.7 (on the Pauling scale) corresponds to 50% ionic character, so that a difference greater than 1.7 corresponds to a bond which is predominantly ionic.

The estimated electronegativity difference for 50% of ionic bond character is 1.7. For $\ce{Ti-C}$ is 0.92, for $\ce{Sc-P}$ it is 0.83, therefore the covalent bond character is dominant.

Element	Pauling electronegativity	Electronegativity difference
Ti	1.63	0.92
C	2.55
Sc	1.36	0.83
P	2.19

Answer 2

As Poutnik describes in his answer, low-electronegativity nonmetallic such as boron form bonds with low ionic character because in general, their atoms are not strongly electronegative enough to fully withdraw electrons even from highly electropositive metals (which still do require some ionization energy).

Nonetheless, incorporating such atoms into structures whose molecular orbitals are more strongly electron-accepting than the individual atomic orbitals can lead to compounds having more ionic character. For instance, in magnesium diboride ($\ce{MgB2}$) the boron atoms are arranged in sheets isostructural with graphite layers, but the boron atoms offer only three electrons apiece whereas the carbon in normal graphite layers offer four. The resulting electron deficiency means the boron is easier to ionize negatively, as indicated in this answer:

Nishibori et al. [1] found that at room temperature, magnesium is essentially fully ionized to Mg2+ while the boron remains neutral; the negative charge is associated with the interstitial regions as if to constitute metallic bonds. This still represents two-thirds of the theoretical charge separation for an ionic model and in that sense, the bonding between magnesium and boron may be deemed predominantly ionic. At 15 K the electrons become more localized so the boron now has a significant negative charge and the percentage of theoretical charge separation exceeds 80%.

Cited Reference

1. Eiji Nishibori, Masaki Takata, Makoto Sakata, Hiroshi Tanaka, Takahiro Muranaka and Jun Akimitsu, "Bonding Nature in MgB2", Journal of the Physical Society of Japan 70:8 (2001), 2252-2254, https://doi.org/10.1143/JPSJ.70.2252.