Section 2.1: The Nature of Matter Adapted from Teacher: Mrs. Rolle Structure of Atom Section 2.1: The Nature of Matter Adapted from Teacher: Mrs. Rolle

What is an atom? Atoms are the “building blocks” or “smallest unit “of matter.

Atomic Structure

Atomic Structure Nucleus Electron cloud/orbit Protons Neutrons Electrons

Atomic Structure Electrons Tiny, very light particles (do not count mass) Have a negative electrical charge (-) Move around the outside of the nucleus

Atomic Structure Protons Much larger and heavier than electrons Protons have a positive charge (+) Located in the nucleus of the atom 

Atomic Structure Neutrons Large and heavy like protons Neutrons have no electrical charge Located in the nucleus of the atom 

Atomic Structure ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

The Atom Electron Nucleus Shell or Orbit

If all atoms are made of protons, neutrons, & electrons, why do different atoms have different chemical properties?

Answer- It’s dependent upon the number and the arrangement of… Electrons! Electrons are the parts of atoms that are affected by chemical reactions! Atoms of different elements have different numbers of electrons, protons, and neutrons!

Look at your periodic table

Differentiating Atoms Atomic Number-Number of protons in the nucleus-determines the type of atom Since atoms are electrically neutral, the number of protons = number of electrons Mass Number Number of protons + neutrons in the nucleus Usually very close to the atomic mass BUT it’s not the same thing! Protons + neutrons= mass

Reading the Periodic Table Mass

How to determine the # of p, n, e? Atomic # = # of protons- determines the atom Atomic mass = # of protons + neutrons In neutral atoms: #protons = electrons & many times neutrons To determine # of neutrons: average mass (weight) - # of protons

Let’s practice

Mass and atomic number 2 He 4 Particle Relative Mass Relative Charge Proton 1 Neutron Electron -1 He 2 4 PROTON NUMBER = number of protons (obviously) SYMBOL MASS NUMBER = number of protons + number of neutrons

The Atom Hydrogen Proton Electron Hydrogen has one proton, one electron and NO neutrons

The Atom Helium Proton Electron Neutron Helium has two electrons, two protons and two neutrons

The Atom Helium Proton Electron Neutron Helium has two electrons, two protons and two neutrons

The Atom Lithium Electrons Protons Neutrons

The Atom Beryllium Electrons Protons Neutrons Beryllium has four electrons, four protons and five neutrons.

The Atom Boron Electrons Protons Neutrons Boron has five electrons, five protons and six neutrons.

The Atom Carbon Electrons Protons Neutrons Carbon has six electrons, six protons and six neutrons.

The Atom Nitrogen Electrons Protons Neutrons Nitrogen has seven electrons, seven protons and seven neutrons.

The Atom Oxygen Electrons Protons Neutrons Oxygen has eight electrons, eight protons and eight neutrons.

The Atom Fluorine Electrons Protons Neutrons Fluorine has nine electrons, nine protons and ten neutrons.

The Atom Neon Electrons Protons Neutrons Neon has ten electrons, ten protons and ten neutrons.

Review Atomic # = # of protons- determines the atom Atomic mass = # of protons + neutrons In neutral atoms: #protons = electrons & many times neutrons To determine # of neutrons: atomic weight - # of protons

Isotopes Atoms with the same number of protons but different numbers on neutrons Example: Carbon So you can change the number of neutrons and the element still maintains its identity

# p+ #e- #n0 126C 6 12-6 = 6 23892U 92 238-92 = 146 3215P 15 32-15 = 17

Review # protons- 6 # electrons-6 # of neutrons-6

Review # protons- 80 # electrons-80 # of neutrons-120