Chap 02 Part 2

Questions and Answers

What is the correct formula for Magnesium oxide?

MgO (correct)

MgO2

Mg2O

MgO3

Which compound has the formula H2O?

Hydrogen chloride

Hydrogen gas

Oxygen gas

Water (correct)

What happens to the valency when writing the formula for a compound?

Valencies are multiplied.

Valencies are interchanged. (correct)

Valencies are added together.

Valencies are ignored.

Which of the following is the correct formula for Carbon dioxide?

CO2 Signup and view all the answers

In which formula are the subscripts not written?

Hydrogen chloride Signup and view all the answers

What is the valency of Hydrogen when writing chemical formulae?

1 Signup and view all the answers

What is the formula for Ammonia?

NH3 Signup and view all the answers

Which combination represents the constituents of Common salt?

Sodium and chlorine Signup and view all the answers

What does the subscript in a molecular formula indicate?

The number of atoms of that element in one molecule. Signup and view all the answers

Which of the following elements has a valency of 2?

Oxygen Signup and view all the answers

What is the molecular formula for a water molecule?

H2O Signup and view all the answers

Which element has the molecular formula S8?

Sulphur Signup and view all the answers

How many atoms of nitrogen are in one molecule of nitrogen gas N2

2 Signup and view all the answers

What is needed to write a molecular formula?

The symbols of the elements and their valency. Signup and view all the answers

What characterizes a molecule compared to an atom?

Molecules can be subdivided into atoms. Signup and view all the answers

Which of the following best defines atomicity?

The number of atoms present in a molecule of an element. Signup and view all the answers

Which of the following pairs of elements are both diatomic?

Hydrogen and Oxygen Signup and view all the answers

What type of molecular structure do noble gases have?

Monoatomic Signup and view all the answers

Which statement about atoms is correct?

Atoms do not exist independently. Signup and view all the answers

What distinguishes polyatomic molecules from diatomic molecules?

Polyatomic molecules contain more than two atoms. Signup and view all the answers

Which molecule is classified as triatomic?

Ozone Signup and view all the answers

How is a water molecule composed?

2 atoms of hydrogen and 1 atom of oxygen Signup and view all the answers

What does a molecular formula indicate?

The composition of a molecule Signup and view all the answers

Which of the following compounds is polyatomic?

Phosphorus Signup and view all the answers

What is the molecular formula representation for hydrogen chloride?

H-Cl Signup and view all the answers

Which statement about diatomic molecules is correct?

They consist of two atoms. Signup and view all the answers

How many atoms are in a molecule of carbon dioxide?

1 atom of carbon and 2 atoms of oxygen Signup and view all the answers

What distinguishes molecules of an element from compounds?

Compounds are made up of two or more different elements. Signup and view all the answers

Which statement accurately defines a compound?

A compound is made of two or more elements chemically combined in a fixed ratio. Signup and view all the answers

What is the correct description of an atom?

An atom is the smallest particle that retains properties of an element. Signup and view all the answers

What represents the composition of a molecule?

The molecular formula. Signup and view all the answers

Which of the following is NOT a classification of elements?

Transitional metals Signup and view all the answers

What distinguishes an element from a compound?

Elements consist of one type of particle, whereas compounds consist of two or more types. Signup and view all the answers

Which statement best describes an atom?

It is the smallest particle of an element that retains its properties. Signup and view all the answers

What distinguishes molecules from atoms?

Molecules can exist independently. Signup and view all the answers

What is true about the atoms of different elements?

They differ in mass and chemical behavior. Signup and view all the answers

Which of the following best describes noble gases?

They can exist as single atoms. Signup and view all the answers

How are molecules formed?

By a combination of atoms of the same or different elements. Signup and view all the answers

Which property is maintained by an atom during physical and chemical changes?

Its distinct properties as an element. Signup and view all the answers

What is a characteristic feature of a compound's molecule?

It is formed by the combination of different atoms. Signup and view all the answers

The term 'atom' derives from which Greek word, and what does it imply?

Atomos, meaning 'uncuttable'. Signup and view all the answers

Study Notes

Atoms and Molecules

An atom is the smallest particle of an element that possesses all the properties of that element and may or may not have independent existence.
Atoms of most elements are very reactive and do not exist as free atoms; they exist in combination with the atoms of the same element or other elements.
All atoms of an element are similar or identical and exhibit the same properties.
The atoms of one element are different from those of other elements and have different properties.
An atom maintains its properties through all physical and chemical changes.

Molecules

A molecule is the smallest particle of an element or a compound that has independent existence and shows all the properties of that substance.
Molecules are formed by the combination of the atoms of the same element or of different elements.
A molecule of a compound has atoms of different elements combined in a fixed whole-number ratio.
The atoms in a molecule are held together by attractive forces called chemical bonds.

Elements

An element is a pure substance that cannot be broken down into simpler substances by any physical or ordinary chemical means.
Elements can be classified into metals, non-metals, metalloids, and noble or inert gases based on their properties.
The symbol of an element is a single-letter or two-letter abbreviation (short name) of its full name.

Compounds

A compound is a substance made up of two or more elements chemically combined together in a fixed ratio.
The formula of a compound shows the number of atoms of different elements present in one molecule of that compound.
The combining capacity of an element is known as its valency, which is used to find out how the atoms of an element will combine with the atoms of another element to form a compound.

Molecular Formula

The molecular formula represents the composition of a molecule of an element or a compound.
The molecular formula of an element shows the number of atoms present in one molecule of that element.
The molecular formula of a compound shows the number of atoms of different elements present in one molecule of that compound.

Subscript

The subscript in a molecular formula tells us how many atoms are present in one molecule of that element.
The subscript is a small number written below and to the right of the symbol of the element.

Atomicity

The number of atoms present in a molecule of an element is called its atomicity.
Elements such as helium, neon, and argon exist as single atoms and are called monoatomic molecules.
Elements such as oxygen, hydrogen, and nitrogen exist as diatomic molecules, meaning their molecules are composed of two atoms.
Molecules containing more than two atoms are polyatomic.

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Learn about the properties of atoms, their reactivity, and how they combine with others to form molecules.

Chap 02 Part 2 - Atoms