Chapter 1: Atomic Structure and the Periodic Table 1.1 Atoms are the smallest form of elements. • All matter is made of atoms. About 100 different atoms, or elements, make up everything on Earth. Hydrogen is the most abundant element in the universe, it makes up 90% of all elements in the universe . Oxygen is the most abundant element in the human body and in Earth's crust . • The structure of an atom
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Chapter 1: Atomic Structure and the
Periodic Table
1.1 Atoms are the smallest form of elements.
• All matter is made of atoms. About 100
different atoms, or elements, make up
everything on Earth.
Hydrogen is the most abundant element
in the universe, it makes up 90% of all
elements in the universe.
Oxygen is the most abundant element in
the human body and in Earth's crust.
• The structure of an atom
• Nucleus: is at the center of the atom, and is a
combination of protons and neutrons.
Protons: are positively charged particles.
Neutrons: are particles that have NO
electrical charge.
Protons and neutrons have approximately
the same mass.
Electrons: are tiny particles with a
negative charge.
o They form a cloud, because at the same time
that they repel each other, they are attracted to
the positively charged protons in the nucleus.
(2000 times smaller than protons and
neutrons)
What part of the atom has a positive
charge, negative charge and no charge?
What is the smallest sub-atomic particle?
• Atomic Number: is the number of protons in
an atom’s nucleus.
• Atomic mass number: is the combined
number of protons and neutrons in a nucleus.
• Isotopes: are atoms of an element that have a
different number of neutrons.
For example, most carbon atoms contain 6
protons and 6 neutrons. Some carbon
atoms, however, have 6 protons and 8
neutrons.
Chemists will often put the atomic mass
number after the element's name, such as
carbon-12 or carbon-14, to signify
different isotopes.
How would we write these isotopes? What is
the difference between each isotope?
Atomic Mass: of an element is the average
mass of all the element’s isotopes.
• Ions are atoms that have lost or gained one or
more electrons.
They no longer contain equal numbers of
protons and electrons, so they have an
electric charge.
Atoms that have lost electrons are
positive ions; atoms that have gained
electrons are negative ions.
1.2 Elements make up the periodic table.
• Mendeleev’s Periodic Table
A Russian chemist, Dmitri Mendeleev,
was the first to produce a periodic table
of the elements.
His periodic table was organized by
increasing atomic mass and similarities in
chemical properties.
The Na atom is now Na+ because it has one more positive proton than negative electrons.
Sodium ion (Na+) 11 protons & 10 electrons
Sodium atom (Na) 11 protons & 11 electrons
An electron is lost
An electron is gained
Chlorine atom (Cl) 17 protons & 17 electrons
Chlorine atom (Cl-) 17 protons & 18 electrons
The Cl atom is now Cl-
because it has one more negative electron than positive proton.