,Introduction
Chemical evolution is the leading explanation for the origin of life on Earth .
·
Inputs of energy led to formation of increasingly complex
Carbon-containing molecules .
·
Eventually led to a molecule that could replicate itself .
·
switch from chemical to biological evolution .
Evolution by natural selection took over.
A descendant of the original molecule became metabolically active and
acquired a membrane .
Life had begun .
The building blocks of chemical evolution .
Just four types of atoms make up 96.% of matter in organisms
hydrogen , Carbon , nitrogen , and oxygen .
The physical structure of these atoms are composed of :
1) protons positively charged particles .
Electron
2) Neutrons neutral particles . ·
·. ProtonNucle
negatively charged particles .
s
3) Electrons
Protons and neutrons are located in the nucleus . o ⑯
Electrons are found in orbitals surrounding the nucleus .
The atomic number is the characteristic number of protons in the nucleus
of any atom .
Also known as proton number.
It is written as a subscript to the left of its Symbol .
Atoms with the same atomic number have the same chemical properties
and belong to the same element.
protons have a (t) charge and electrons have a C-) charge . When an atom
has an equal number of protons and electrons , the charges balance and
the entire atom is electrically neutral .
The mass number is the number of protons + neutrons in an atom .
Also known as nucleon number.
It is written as a superscript to the left of its Symbol .
Each proton and each neutron has a mass of one dalton (Da).
The mass of an electron is so small , it can be ignored . Therefore , the
mass of an atom is equal to its mass number .
mass number
Atomic number He
, Isotopes are forms of an element with different numbers of neutrons
and different masses but same number of proton .CCC
The atomic weight of an element is the average of all the masses of the
naturally occurring isotopes based on their abundance.
The atomic number of Carbon is 12 01 .
, Since Carbon-12 is the most
abundant isotope .
Carbon , nitrogen , oxygen , phosphorus , sulfur and hydrogen are the
most abundant element found in organisms .
Most isotopes are stable , but some are unstable radioactive isotopes that
decay over time .
Electrons move around atomic nuclei in specific regions called orbitals .
Orbitals are grouped into levels called electron shells .
Electron shells are numbered 1 , 2 , 3 and so on . The numbers indicate
their relative distance from the nucleus , the smaller numbers are closer
to the nucleus .
Each electron shell contains a specific number of orbitals .
·
An electron shell comprising a single orbital can hold up to 2 electrons .
·
A shell with four orbitals can contain up to selectrons .
The electrons of an atom fill the innermost shells first and then fill the
outer shells .
The outermost shell of an atom is the valence shell . Electrons in this shell
are valence electrons .
The number of unpaired valence electrons is called the valence of an atom .
Different atoms have different numbers of unpaired electrons .
How does covalent bonding hold molecules together ?
Atoms are most stable when their valence shells are full .
shells can be filled by formation of chemical bonds .
·
Attractions that bind atoms together.
·
covalent bonds form when unpaired valence electrons are shared by
2 atoms . This effectively gives each atom a full outer shell .
covalent bond
&
HH
D
↑ H H
.
Hydrogen atom each have one Ha molecule has 2
unpaired electron Shared electron
Chemical evolution is the leading explanation for the origin of life on Earth .
·
Inputs of energy led to formation of increasingly complex
Carbon-containing molecules .
·
Eventually led to a molecule that could replicate itself .
·
switch from chemical to biological evolution .
Evolution by natural selection took over.
A descendant of the original molecule became metabolically active and
acquired a membrane .
Life had begun .
The building blocks of chemical evolution .
Just four types of atoms make up 96.% of matter in organisms
hydrogen , Carbon , nitrogen , and oxygen .
The physical structure of these atoms are composed of :
1) protons positively charged particles .
Electron
2) Neutrons neutral particles . ·
·. ProtonNucle
negatively charged particles .
s
3) Electrons
Protons and neutrons are located in the nucleus . o ⑯
Electrons are found in orbitals surrounding the nucleus .
The atomic number is the characteristic number of protons in the nucleus
of any atom .
Also known as proton number.
It is written as a subscript to the left of its Symbol .
Atoms with the same atomic number have the same chemical properties
and belong to the same element.
protons have a (t) charge and electrons have a C-) charge . When an atom
has an equal number of protons and electrons , the charges balance and
the entire atom is electrically neutral .
The mass number is the number of protons + neutrons in an atom .
Also known as nucleon number.
It is written as a superscript to the left of its Symbol .
Each proton and each neutron has a mass of one dalton (Da).
The mass of an electron is so small , it can be ignored . Therefore , the
mass of an atom is equal to its mass number .
mass number
Atomic number He
, Isotopes are forms of an element with different numbers of neutrons
and different masses but same number of proton .CCC
The atomic weight of an element is the average of all the masses of the
naturally occurring isotopes based on their abundance.
The atomic number of Carbon is 12 01 .
, Since Carbon-12 is the most
abundant isotope .
Carbon , nitrogen , oxygen , phosphorus , sulfur and hydrogen are the
most abundant element found in organisms .
Most isotopes are stable , but some are unstable radioactive isotopes that
decay over time .
Electrons move around atomic nuclei in specific regions called orbitals .
Orbitals are grouped into levels called electron shells .
Electron shells are numbered 1 , 2 , 3 and so on . The numbers indicate
their relative distance from the nucleus , the smaller numbers are closer
to the nucleus .
Each electron shell contains a specific number of orbitals .
·
An electron shell comprising a single orbital can hold up to 2 electrons .
·
A shell with four orbitals can contain up to selectrons .
The electrons of an atom fill the innermost shells first and then fill the
outer shells .
The outermost shell of an atom is the valence shell . Electrons in this shell
are valence electrons .
The number of unpaired valence electrons is called the valence of an atom .
Different atoms have different numbers of unpaired electrons .
How does covalent bonding hold molecules together ?
Atoms are most stable when their valence shells are full .
shells can be filled by formation of chemical bonds .
·
Attractions that bind atoms together.
·
covalent bonds form when unpaired valence electrons are shared by
2 atoms . This effectively gives each atom a full outer shell .
covalent bond
&
HH
D
↑ H H
.
Hydrogen atom each have one Ha molecule has 2
unpaired electron Shared electron
