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A formula unit is the simplest formula of an ionic compound and therefore you can think of it as the empirical formula of an ionic compound. But since salts are a repeating solid lattice of ions there is no "molecule" and therefore no "molecular formula" for salts. Examples of formula units: NaCl MgCl 2
Formula unit refers to the smallest group/ratio of atoms that establishes a compound. Does Na+ + Cl-, NaCl, better describe sodium chloride. In the solid form of this salt, in the crystal lattice what if the smallest unit in which you can describe the lattice?
I think that, when discussing calculations, the difference between atoms, molecules, and formula units is not important. In any problem that asks you to solve for a certain amount of any of these, you would multiply the number of moles by Avogadro's constant, 6.022 x 10^23. To break down the differences: An atom is a single unit, like an element.
Formula units are basically empirical formulas for ionic compounds, but in most questions just represent molecules (in their simplest, empirical form). For example, E.9 (b) asks for the number of formula units of magnesium sulfate heptahydrate in a 5.15 g sample of the compound.
Formula units are used to describe the simplest, whole number ratio of ions in an ionic compound. So, you're correct in calculating the number of moles and then using Avogadro's constant (6.022 x 10^23) to find the number of formula units, which also happens to be the number of molecules in a covalent compound.
Answer: A group of ions is called a formula unit. For example, KCl is a formula unit comprised of and . is a formula unit of ions 2 and . If given certain ions, you would be expected to know how to write the formula unit and vice versa.
Similarly, the formula weight would be the molar mass of the ionic compound. To solve for #25a) you would multiply the moles of KNO3 by Avogadro's number to get how many formula units are in 0.750 moles of KNO3. (Answer: 4.52 x 10^23 formula units) 25b) Divide the given formula units by Avogadro's number and then multiply by the molar mass of ...
Ella is absolutely correct about molecules having covalent bonds and formula units having ionic bonds! Formula units are just the smallest ratio an ionic compound can exist in. Formula units are special because ionic compounds can take on complex crystalline structures which is defined as some repeating combination of formula units.
Zeff is effective nuclear charge. We can use the formula Zeff = Z - S where Z is the atomic number and S is the shielding constant to calculate the effective nuclear charge. Generally, effective nuclear charge increases across a row as the number of protons in the center of the atom increases and pulls more on the outer electrons.
The difference between molar mass and formula mass is that formula mass is the sum of all the atomic weights of the atoms in its empirical formula while molar mass is just the mass of 1 mol of a substance. Molar mass also uses the units g/mol while formula mass uses atomic mass units (amu).