Atoms, Ions, and Molecules

Think about it…

• What do a frog, a skyscraper, a car, and your body all have in common?

ATOMS!

• Every physical thing you can think of, living or not, is made of incredibly small particles called atoms.

The atom

• The small basic unit of _____________.

–Matter – anything that takes

up space and has mass

• How small is an atom??– Millions and millions of atoms could fit in the space

the size of the period at the end of this sentence.

Atoms consist of three types of smaller particles:

• Protons (+)• Neutrons (neutral)• Electrons (-)

• Notice the locationof protons, neutrons,and electrons in an atom

Element• Element – type of atom that can’t be broken

down into a simpler substance

• Examples of elements:– Hydrogen– Lithium– Carbon– Boron

How do we identify an element?

Answer = by the number of protons

Think about it: if Krypton loses a proton, is it still Krypton??

Atomic Number = number of protons

• How can we identify the number of:• Protons = ____________• Neutrons = ___________• Electrons = ___________

• From this picture?

Atomic Number = number of protons

**Number of protons and electrons is the same

Atomic Weight

To find the number of neutrons you have to find the mass number. To find the mass number, all you need to do is round the atomic weight to the nearest whole number. In our example, krypton's mass number is 84 since its atomic weight, 83.80, rounds up to 84.

THEN complete the formula below:Mass Number = (Number of Protons) + (Number of Neutrons)

84 = (36) + (??)

Elements

What four elements make up 96% of a human’s body mass??1.)2.)3.)4.)

Elements

What four elements make up 96% of a human’s body mass??1.) Carbon2.) Oxygen3.) Nitrogen4.) Hydrogen

Review

– Where are protons and neutrons found in the atom?

– Where are the electrons found in the atom?

The Bohr Model• Niels Bohr introduced “The Bohr Model” in 1913• Model that shows the atoms electrons located

outside the nucleus in regions called energy levels (valence shell) Energy levels

The Bohr Model• The first energy level can ONLY have up to 2

electrons• The remaining energy levels can have up to 8

Energy level

Practice• Draw a Bohr model of an oxygen and calcium

carbon atom.

Figure 2.3 Electron configurations-overview

Isotope – same number of protons (same element) different number of neutrons (different mass)

Example: Carbon 12, Carbon 13, Carbon 14

Figure 2.2 Nuclei of the three naturally occurring isotopes of carbon-overview

When atoms gain or lose electrons

• Ions – an atom that gained or lost one or more electrons is called an ion

• Why do atoms gain or lose electrons?– Atoms want a full outermost energy level (valence

shell)– When an atom loses or gains electrons it has an

electrical charge (positive or negative)

For example: • Sodium (Na) has how many electrons?• Chlorine (Cl) has how many electrons?

Draw the Bohr model for each

Who is closer to having a full outermost electron shell??

• Na will give one of its electrons to chlorine– Becomes Na+ = positive charge = cation

• Cl will gain an electron from Na – Becomes Cl- = negative charge = anion

Why are Ions important?

• Hydrogen ions (H+) are needed for the production of usable chemical energy in cells

• Calcium ions (Ca2+) are necessary for every muscle movement in your body

• Chloride ions (Cl-) are important for sending chemical signals to your brain

Ionic Bonds

• Forms through the electrical force between oppositely charged ions

• Think back to NaCl that we just talked about

Ionic Bond

• Have you ever heard positive and negative attract?• It’s the same here!• Na+ attracts to Cl-• NaCl = table salt

The positive sodium ion (Na+) and negative chloride ion (Cl-) attract to each other and form an ionic bond

BUT, Not all atoms easily gain or lose electrons…

• It is possible for atoms to share electrons• A covalent bond forms when atoms share a

pair of electrons• Draw a Bohr model for oxygen and carbon

– How many electrons does oxygen need to fill its outermost shell?

– How many electrons does carbon need to fill its outermost shell?

Carbon dioxide (CO2) is a covalent bond

• An oxygen atom needs two electrons to fill its outer energy level. A carbon atom needs 4 electrons to fill its outer energy level. In carbon dioxide, carbon makes a double bond, or SHARES two pairs of electrons with each oxygen atom

Water (H2O) is a covalent bond

What is a molecule?

• Molecule- two or more atoms held together by covalent bonds

For example: H2O, CO2, O2, etc.

**Almost all of the substances that make up organisms are molecules held together by covalent bonds

Compounds

• A substance made of different elements bonded together in a certain ratio

• Held together by chemical bonds

• H2O, CO2, NaCl….can you think of any others?