4. Write answers
to the following
questions and explain your answers.
a. Explain how the element sodium is
monovalent.
b. M is a bivalent metal. Write down
the steps to find the chemical
formulae of its compounds formed
with the radicals, sulphate and
phosphate
c. Explain the need for a reference
atom for atomic mass. Give some
information about two reference
atoms.
d. What is meant by Unified Atomic
Mass.'
e. Explain with examples what is
meant by a 'mole' of a substance.
Answers
Answer:
ans)a)
Sodium has one electron in its valence shell and needs to remove it to attain noble gas configuration. So, it gets ionizes and gives one electron to another compound to form a compound. Thus, it has a valency of 1 and is called as a monovalent atom.
ans)b)
M is bivalent metal means it has valency 2. Beryllium, Magnesium, Calcium,Scandium, Barium, Radium are metals having valency 2.
To write chemical formula of any compound the simplest method is criss cross method.
In this method
Step 1: we will take Magnesium to form compound with sulphate.
Step 2: First we should know the component of compound that are magnesium and sulphur. Step 3: Now we have to write the valency of both components that is of magnesium 2 as it is bivalent and of sulphur is 2 as it belongs to halogen family.
Step 4: Now we have to criss cross.
We get MgSO4
ans)c)
Atomic mass is the is the sum of the electrons and the neutrons in the atom. Number of electrons is the atomic number. Hence to determine the atomic mass the reference of the atom is required. Example to find the atomic mass of atom magnesium Mg we need to know the atomic number of magnesium.
ans)d)
931.49410242(28) The dalton or unified atomic mass unit (symbols: Da or u) is a unit of mass widely used in physics and chemistry. It is defined as 1/12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest.
ans)e)
A mole corresponds to the mass of a substance that contains 6.023 x 1023 particles of the substance. The mole is the SI unit for the amount of a substance. Its symbol is mol. By definition: 1 mol of carbon-12 has a mass of 12 grams and contains 6.022140857 x 1023 of carbon atoms (to 10 significant figures).
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Answer:
substances like glucose, water and ammonia are made up of different elements. Such substances are called compounds. Like elements, compounds too are pure substances that cannot be easily broken down by simple physical methods.
Water is made up of two kinds of atoms- hydrogen and oxygen. The formula of water molecule is H2O. as you see, in a molecule of water there are 2 atoms of hydrogen and 1 atom of oxygen. Similary, in ammonia, one atom of nitrogen combines with three atoms of hydrogen to form the compound ammonia (NH3); so there is 1 nitrogen atom and 3 hydrogen atoms in the molecule.
Explanation: