1. Answer;
Mass
Mendeleev arranged the known chemical elements in a table according to increasing mass.
Step-by-step explanation;
- Mendeleev arranged the elements in rows in order of increasing mass so that elements with similar properties were in the same column. He provided an organizing principle that worked for all off the known elements.
- The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be. He also left spaces for undiscovered elements in order to place elements with similar properties in the same column.
- Mendeleev's periodic table was useful because it enabled scientists to predict properties of unknown elements.
2. Answer;
Atomic mass unit.
One twelfth the mass of a carbon-12 atom is used to define an atomic mass unit
Step-by-step explanation;
- An atomic mass unit (AMU) refers to precisely 1/12 the mass of an atom of carbon-12. The carbon-12 atom has six protons and six neutrons in its nucleus. One AMU is the average of the proton rest mass and the neutron rest mass.
- The mass of an atom in atomic mass unit is approximately equal to the sum of the number of protons and neutrons in the nucleus.
- The atomic mass unit expresses the relative masses of various isotopes of elements.
3. Answer;
Five electrons
A member of the boron family has three valence electrons, while a member of the nitrogen family has five electrons.
Step-by-step explanation;
- The number of valence electrons is the number of electrons in the outermost energy level of an atom.
- Nitrogen family includes, non-metals, metalloids, and metals. The atoms of these elements in the nitrogen family have a 5 valence electrons. The family include elements, phosphorus, bismuth, arsenic and antimony. They form bonds through sharing of electrons.
4. Answer;
Li2O
Explanation;
- Ionic compounds are compounds that are made up of ions. They are formed as a result of transfer of electrons from one atom to another. One atom loses electrons while the other atom gains electrons, resulting to formation of negatively charged ion (anion) and positively charged ion (cation) which join via ionic bond to form an ionic compound.
- Lithium oxide is an example of ionic compound formed from lithium and oxygen atoms. Lithium has a valency of one while oxygen has a valency of two, therefore, the chemical formula of lithium oxide will be Li2O.
5. Answer;
Of the strong attractions between polar water molecules
Water has a higher boiling point than expected because of the strong attractions between polar molecules.
Explanation;
- Water has a high boiling point because of intermolecular forces of attraction called hydrogen bonds. Hydrogen bonding is a form of dipole-dipole interaction, where a molecule that is partially positive is attracted to another molecule that is partially negative.
- Hydrogen bond being a powerful intermolecular force, it makes water to have a high boiling point, because they require more energy to break the bond.