Atoms and Elements

The Nature of Matter Matter refers to anything that takes up space and has mass. Matter refers to anything that takes up space and has mass. Matter is composed of elements, substances that cannot be broken down into another substance. Matter is composed of elements, substances that cannot be broken down into another substance. There are 92 natural elements. There are 92 natural elements. Living organisms are made primarily of six elements. Living organisms are made primarily of six elements.

The Nature of Matter

Elements: Made up of tiny particles called atoms Made up of tiny particles called atoms Each has its own Each has its own name name atomic number atomic number atomic symbol atomic symbol Name Number Symbol Hydrogen 1 H Aluminum 13 Al Sodium 11 Na

Atomic Structure Atomic Structure Atoms have three main sub atomic structures : Name Charge Mass Location Proton + 1 amu inside nucleus Electron - 1/1837 amu around nucleus Neutron o 1 amu inside nucleus

Atomic Structure All atoms of the same element have the same number of protons It is also equal to the atomic number

The Periodic Table The elements are organized to form the periodic table. The elements are organized to form the periodic table. The columns in the table are groups. The columns in the table are groups. The rows in the table are periods. The rows in the table are periods. Elements in groups have similar chemical and physical characteristics. Elements in groups have similar chemical and physical characteristics.

The Periodic Table

Atomic Structure The Atomic Mass is the number of protons plus neutrons The electrons are so small they are not included in the mass Atomic Number N 15 7 Mass Number of protons: 7 Number of neutrons: 8 Atomic mass: 15

Review: Finding Atomic Parts To find the number of protons – To find the number of protons – Proton # = Atomic number on periodic chart Proton # = Atomic number on periodic chart To find the number of electrons – To find the number of electrons – Electron # = Atomic number on periodic chart Electron # = Atomic number on periodic chart To find the number of neutrons – To find the number of neutrons – Neutron # = Atomic mass (rounded) minus atomic number Neutron # = Atomic mass (rounded) minus atomic number

Review: Finding Atomic Parts Atomic Number Na Mass Number of protons: 11 (= atomic #) Number of electrons: 11 (= atomic #) Number of neutrons: 12 (atomic mass 23 – atomic number 11) (atomic mass 23 – atomic number 11) Sodium Atomic Particles:

Composition of Matter- Elements Symbols to know: Symbols to know: C Carbon Na Sodium Mg Magnesium O Oxygen P Phosphorus Fe Iron H Hydrogen S SulfurCa Calcium N Nitrogen Cl Chlorine K Potassium

Composition of Matter- Elements Why are the atomic mass units on the periodic chart not whole numbers? Some atoms of an element are heavier or lighter than others – Atoms of the same element with different masses are called ISOTOPES The atomic mass on the chart is a weighted average of all of the known masses

Composition of Matter- Elements Isotopes Isotopes have the same atomic number but a different atomic mass Atoms of the same element must have the same number of protons. The difference in mass comes from a different number of neutrons

Composition of Matter- Elements Isotopes: Isotopes: Atom #1: 7 protons, 7 neutrons Atom #1: 7 protons, 7 neutrons Atom #2: 7 protons, 8 neutrons Atom #2: 7 protons, 8 neutrons Not isotopes: Not isotopes: Atom #1: 7 protons, 7 neutrons Atom #1: 7 protons, 7 neutrons Atom #2: 8 protons, 8 neutrons Atom #2: 8 protons, 8 neutrons Since these two atoms have a different number of protons, they are two different elements, not isotopes

Composition of Matter- Elements Isotopes are represented differently, showing their atomic mass. Examples: carbon – 14 is an isotope of carbon with a mass of 14 (the normal mass is 12) iodine – 131 is an isotope of iodine with a mass of 131 (the normal mass is 127)

Composition of Matter- Elements Radioactive isotopes or radioisotopes: isotopes that are very unstable and release energy as they “fall apart” or disintegrate. isotopes that are very unstable and release energy as they “fall apart” or disintegrate. This radiation can be detected with a Geiger counter.

Uses of Radioactive Isotopes Radioactive isotopes can be used as tracers to follow the movement of that element through chemical reactions. Radioactive isotopes can be used as tracers to follow the movement of that element through chemical reactions. Radioactive isotopes can be used to sterilize medical and dental instruments. Radioactive isotopes can be used to sterilize medical and dental instruments. Radioactive isotopes can also be used to kill cancer cells. Radioactive isotopes can also be used to kill cancer cells.

Uses of Radioactive Isotopes

Atomic Structure Electrons are found in energy levels outside the nucleus Electrons are found in energy levels outside the nucleus The first energy level holds two electrons The first energy level holds two electrons The second energy level holds eight electrons The second energy level holds eight electrons The third energy level holds eight electrons The third energy level holds eight electrons Other levels can hold more Other levels can hold more Octet Rule: Stable atoms have eight electrons in their outer level Octet Rule: Stable atoms have eight electrons in their outer level

Arrangements of Electrons in an Atom

To Draw an Atom List the number of protons, electrons and protons List the number of protons, electrons and protons List the number of electrons to draw in each energy level List the number of electrons to draw in each energy level Write the number of protons and neutrons in the center (nucleus) of the atom Write the number of protons and neutrons in the center (nucleus) of the atom Draw the electrons on circles around the nucleus Draw the electrons on circles around the nucleus Example: Sodium Atomic # = 11 Atomic mass = 23 P= 11 E = 11 N = 12 Electron levels: First = 2 First = 2 Second = 8 = 11 Third = 1 P = 11 N = 12

Atomic Structure Electrons in the outermost shell are called valence electrons Electrons in the outermost shell are called valence electrons The valence electrons determine how an element will react The valence electrons determine how an element will react All elements in the same column (group) of the Periodic table have the same number of valence electrons All elements in the same column (group) of the Periodic table have the same number of valence electrons Oxygen has six valence electrons Oxygen has six valence electrons