Introduction to Atoms and Molecules
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Questions and Answers

What are the basic building blocks of matter?

Atoms

What are formed when two or more atoms combine chemically?

Molecules

Atoms are mostly filled with matter.

False

What is the central part of an atom called?

<p>Nucleus</p> Signup and view all the answers

What type of charge do protons have?

<p>Positive</p> Signup and view all the answers

What is the number of protons in an atom's nucleus equal to?

<p>Atomic number</p> Signup and view all the answers

What is the total number of protons and neutrons in an atom's nucleus called?

<p>Mass number</p> Signup and view all the answers

In a neutral atom, what is the number of electrons equal to?

<p>Number of protons</p> Signup and view all the answers

What are the different energy levels that electrons orbit called?

<p>Shells or orbitals</p> Signup and view all the answers

What are the electrons in the outermost shell called, and what do they determine?

<p>Valence electrons</p> Signup and view all the answers

What is atomic mass measured in?

<p>Atomic mass units (amu)</p> Signup and view all the answers

Atomic mass is the mass of a single, specific isotope of an element.

<p>False</p> Signup and view all the answers

How are elements represented?

<p>Symbols</p> Signup and view all the answers

How are compounds represented?

<p>Chemical formulae</p> Signup and view all the answers

What does the chemical formula H₂O represent?

<p>Water</p> Signup and view all the answers

What is the sum of the atomic masses of all the atoms in a molecule called?

<p>Molecular mass</p> Signup and view all the answers

What unit is used to measure the amount of a substance?

<p>Mole</p> Signup and view all the answers

What is Avogadro's constant?

<p>6.022 × 10²³</p> Signup and view all the answers

One mole of any substance contains the same number of particles.

<p>True</p> Signup and view all the answers

What is the mass of one mole of a substance numerically equal to?

<p>Relative atomic or molecular mass</p> Signup and view all the answers

What does percentage composition refer to?

<p>Percentage by mass of each element in a compound</p> Signup and view all the answers

What does an empirical formula show?

<p>Simplest whole-number ratio of atoms in a compound</p> Signup and view all the answers

What does a molecular formula show?

<p>Actual number of atoms of each element in a molecule</p> Signup and view all the answers

A molecular formula can be the same as the empirical formula.

<p>True</p> Signup and view all the answers

What is a chemical reaction?

<p>Process where reactants change into products</p> Signup and view all the answers

What represents a chemical reaction using symbols and formulae?

<p>Chemical equation</p> Signup and view all the answers

The number of each atom of every element is the same on both sides of a balanced chemical equation.

<p>True</p> Signup and view all the answers

What is the importance of balancing chemical equations?

<p>Satisfying the law of conservation of mass</p> Signup and view all the answers

Study Notes

Introduction to Atoms and Molecules

  • Matter is anything that has mass and occupies space.
  • Matter is made up of extremely tiny particles known as atoms.
  • Atoms are the basic building blocks of matter.
  • Molecules are formed when two or more atoms combine chemically.
  • Atoms are extremely small and are mostly empty space.
  • The nucleus of an atom contains positively charged particles called protons and neutral particles called neutrons.
  • Electrons, negatively charged particles, orbit the nucleus.

Atomic Structure

  • The central part of an atom is called the nucleus.
  • Protons have a positive charge (+1).
  • Neutrons have no charge (0).
  • Electrons have a negative charge (-1).
  • The number of protons in an atom's nucleus is equal to its atomic number.
  • The mass number of an atom is the total number of protons and neutrons in its nucleus.
  • The number of electrons in an atom is equal to the number of protons in a neutral atom.
  • Electrons orbit in different energy levels called shells or orbitals.
  • The electrons in the outermost shell are called valence electrons and determine the chemical properties of an element.

Atomic Mass

  • Atomic mass is the mass of an atom.
  • It is measured in atomic mass units (amu).
  • Atomic mass is the average mass of all isotopes of an element.
  • This average takes into account the relative abundance of different isotopes.

Symbols and Formulae

  • Elements are represented by symbols.
  • Examples include H for hydrogen, O for oxygen, C for carbon, and Na for sodium.
  • Compounds are represented by chemical formulae.
  • A chemical formula shows the symbols of the elements present in a compound and the number of atoms of each element.
  • For example, water (H₂O) indicates two hydrogen atoms and one oxygen atom.
  • The formula represents the composition of the compound.

Molecular Mass

  • Molecular mass is the sum of the atomic masses of all the atoms in a molecule.
  • Molecular mass is expressed in atomic mass units (amu).
  • Calculated by adding atomic masses of all atoms in the given molecule.
  • The molecular mass of oxygen (O₂) = 2 × atomic mass of oxygen.

Mole Concept

  • A mole is a unit of measurement for the amount of a substance.
  • One mole of any substance contains a fixed number of particles.
  • This fixed number is Avogadro's constant, which is approximately 6.022 × 10²³.
  • One mole of any substance contains Avogadro's number of particles.

Mole and Mass

  • The mass of one mole of a substance is numerically equal to the relative atomic or molecular mass.
  • Units are grams per mole (g/mol).
  • Using the molar mass, the mass of a given number of moles can be calculated.

Percentage Composition of Compounds

  • Percentage composition refers to the percentage by mass of each constituent element in a compound.
  • Calculated from the molar mass of the compounds and the individual molar mass of each component.

Empirical Formulae

  • An empirical formula shows the simplest whole-number ratio of atoms present in a compound.
  • The empirical formula provides the relative number of atoms.

Molecular Formulae

  • A molecular formula shows the actual number of atoms of each element present in a molecule of a compound.
  • A molecular formula can be a multiple of the empirical formula.

Chemical Reactions and Equations

  • A chemical reaction is a process in which one or more substances (reactants) change into one or more new substances (products).
  • A chemical equation represents a chemical reaction, using symbols and formulae of substances involved.
  • The number of each atom of every element is the same on both sides of a balanced chemical equation.
  • Balancing chemical equations is important to satisfy the law of conservation of mass.

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Description

Explore the fundamental concepts of atoms and molecules in this quiz. Understand how matter is composed, the structure of atoms, and the roles of protons, neutrons, and electrons. Test your knowledge on atomic structure and the formation of molecules.

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