NAS - Chemistry 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks

2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks

What is matter?

Anything that has mass and occupies space.

What is an element?

A pure substance made of only one kind of atom.

What is an atom?

The smallest unit of an element that retains the element's properties.

Where are protons located?

Inside the nucleus.

Where are neutrons located?

Inside the nucleus.

Where are electrons located?

Outside the nucleus in the electron cloud.

What charge does a proton have?

Positive (+1).

What charge does a neutron have?

No charge (0).

What charge does an electron have?

Negative (−1).

Which particle determines the identity of an element?

Protons.

What is the atomic number?

The number of protons.

What is the mass number?

The total number of protons and neutrons.

How do you calculate neutrons?

Mass number − atomic number.

What is an isotope?

Atoms of the same element with different numbers of neutrons.

What is a radioactive isotope?

An unstable isotope that emits radiation as it decays.

What is an ion?

An atom or molecule with a net electrical charge.

What is a cation?

A positively charged ion formed by losing electrons.

What is an anion?

A negatively charged ion formed by gaining electrons.

What is a molecule?

Two or more atoms chemically bonded together.

What is a compound?

A substance made of two or more different elements chemically combined.

Why does changing the number of protons create a different element?

Because an element's identity is defined by its number of protons.

Why doesn't changing neutrons create a different element?

Because the number of protons stays the same.

Why do electrons determine chemical reactions?

Because they interact with other atoms during bonding.

Why do electrons contribute very little to an atom's mass?

Because each electron has much less mass than a proton or neutron.

Why are isotopes chemically similar?

Because they have the same number of electrons and therefore the same chemical behavior.

Why are some isotopes unstable?

Because their nuclei contain an imbalance of protons and neutrons.

Atomic number vs. mass number

Atomic number = protons. Mass number = protons + neutrons.

Atom vs. ion

Atom = electrically neutral. Ion = electrically charged.

Isotope vs. ion

Isotope = different neutrons. Ion = different electrons.

Element vs. compound

Element = one kind of atom. Compound = two or more different elements bonded together.

Carbon has 6 protons and 8 neutrons. What isotope is it?

Carbon-14.

Oxygen has 8 protons and gains two electrons. What ion forms?

O²⁻.

Sodium loses one electron. What ion forms?

Na⁺.

An atom has 15 protons. What element is it?

Phosphorus.

An atom has 17 protons, 18 electrons, and 20 neutrons. Is it an isotope, an ion, both, or neither?

Both. It is an isotope and a −1 ion.

Atomic number = ?

Number of protons.

Mass number = ?

Protons + neutrons.

Changing protons changes the _____.

Element.

Changing electrons changes the _____.

Charge.

Changing neutrons creates a different _____.

Isotope.

Why do protons determine an element?

Because the number of protons (atomic number) uniquely identifies each element.

Why don't electrons change an element's identity?

Changing electrons only changes the atom's charge, not its identity.

What is a radioisotope?

An unstable isotope that releases radiation as it decays.

Name one biological use of radioisotopes.

Medical imaging, cancer treatment, or biological research.

What is the nucleus?

The dense center of an atom containing protons and neutrons.

Which subatomic particles contribute almost all of an atom's mass?

Protons and neutrons.

Why is most of an atom's volume empty space?

Electrons occupy a large electron cloud around the tiny nucleus.

If atomic number = 8, what element is it?

Oxygen.

If mass number is 23 and atomic number is 11, how many neutrons are present?

12 neutrons.

If an atom has equal numbers of protons and electrons, what is its charge?

Neutral (0).

What happens when an atom loses electrons?

It becomes a positively charged cation.

What happens when an atom gains electrons?

It becomes a negatively charged anion.

Why do opposite charges attract?

Positive and negative charges are electrostatically attracted.

What is chemical bonding?

The attraction that holds atoms together in molecules or compounds.

Can O₂ be called a compound?

No. It is a molecule of one element, not a compound.

Is H₂O a molecule, a compound, or both?

Both.

Is NaCl a molecule?

No. It is an ionic compound.

Which particle is involved directly in chemical reactions?

Electrons.

Why are ions important in biology?

They are essential for nerve impulses, muscle contraction, and fluid balance.

Which ions are especially important for nerve function?

Sodium (Na⁺) and potassium (K⁺).

What ion is essential for muscle contraction?

Calcium (Ca²⁺).

Compare isotope vs ion.

Isotopes differ in neutrons; ions differ in electrons.

True or False: Changing neutrons changes chemical behavior dramatically.

False. Chemical behavior depends mainly on electrons.

Fill in the blank: Mass number = protons + _____.

Neutrons.

Fill in the blank: An atom that gains electrons becomes a(n) _____.

Anion.

An atom has 17 protons, 17 electrons, and 18 neutrons. What element is it?

Chlorine-35.

An atom has 17 protons, 18 electrons, and 18 neutrons. What is its charge?

-1 (Cl⁻).

An atom has 20 protons and 20 neutrons. What is its mass number?

40.

Which subatomic particle has the smallest mass?

Electron.

Why is the nucleus considered dense?

It contains nearly all of the atom's mass in a tiny space.

What determines an atom's chemical properties?

Its electrons, especially the valence electrons.

What are valence electrons?

The outermost electrons involved in bonding.

Why are valence electrons important?

They determine how atoms bond and react.

True or False: Atoms are usually electrically neutral.

True.

True or False: An ion has unequal numbers of protons and electrons.

True.

Losing electrons makes an atom more _____.

Positive.

Gaining electrons makes an atom more _____.

Negative.

Atom vs. molecule

An atom is one particle; a molecule is two or more bonded atoms.

Molecule vs. compound

A molecule may contain the same element; a compound contains different elements.

Why is water a compound?

It contains hydrogen and oxygen.

Name a molecule that is not a compound.

O₂.

Why are atoms called the building blocks of life?

All living things are made from atoms.

The four most abundant elements in living organisms?

Carbon, hydrogen, oxygen, and nitrogen (CHON).

Which element forms the backbone of biological molecules?

Carbon.

Which element is essential in proteins and DNA?

Nitrogen.

Why is changing protons more significant than changing electrons?

It creates a different element.

Why can sodium and chlorine form an ionic compound?

Opposite charges attract after electron transfer.

Do neutrons create ions?

No. Electrons create ions.

Does increasing neutrons change atomic number?

No. Only protons determine atomic number.

CHON stands for?

Carbon, Hydrogen, Oxygen, Nitrogen.

Why do living organisms require atoms?

Atoms are the basic building blocks of all biological molecules.

Which subatomic particle is responsible for forming chemical bonds?

Electrons, especially valence electrons.

What is the difference between a neutral atom and an ion?

A neutral atom has equal protons and electrons; an ion does not.

Can an isotope also be an ion?

Yes. An atom can differ in both neutrons and electrons.

Which changes when an atom becomes an ion?

The number of electrons.

Which changes when an atom becomes an isotope?

The number of neutrons.

Which never changes unless the element changes?

The number of protons.

What does the atomic number identify?

The element.