3A1 Basics of Atomic Structure, Elements, and Chemical Bonds Flashcards
Explore the history and structure of the atom and subatomic particles.
What is an atom?
The smallest fundamental unit of matter that makes up all substances.
Describe the structure of an atom.
Consists of a small, dense nucleus containing protons (positively charged) and neutrons (neutral).
This nucleus is surrounded by electrons (negatively charged) that orbit the nucleus.
Where are protons located in an atom, and what is their charge?
- Location: found in the nucleus
- Charge: positive charge of +1
Compare the mass of the subatomic particles.
- Protons: Approximately 1 amu
- Neutrons: Approximately 1 amu
- Electrons: Negligible mass compared to protons and neutrons
amu - atomic mass unit
What does the atomic number of an atom refer to?
Refers to the number of protons it has.
Where are neutrons located in an atom, and what is their charge?
- Location: in the nucleus
- Charge: no charge; they are neutral
Where are electrons located in an atom, and what is their charge?
- Location: in the electron cloud surrounding the nucleus
- Charge: negative charge of -1
What holds an atom together?
The attraction between the positively charged nucleus and the negatively charged electron cloud.
How are elements defined?
By the number of protons in an atom’s nucleus, known as the atomic number.
Who discovered the electron?
J.J. Thomson
The discovery was in the late 19th century.
Who proposed the planetary model of the atom?
Ernest Rutherford
This was in the early 20th century.
How did Erwin Schrodinger contribute to atomic theory?
He developed the quantum mechanical model of the atom, describing electrons in terms of probability clouds.
The diagram shows an element of nitrogen. From the information provided, state the number of protons, neutrons, and electrons in one atom of Nitogren.
Protons: 7
Neutrons: 7
Electrons: 7
How did atoms form after the Big Bang?
Through the cooling and combination of subatomic particles like protons, neutrons, and electron.
What did Niels Bohr propose about electron orbits?
That electrons orbit the nucleus in fixed energy levels, or shells, and can jump between these levels when gaining or losing energy.
Why are atoms studied using models?
They are too small to be observed directly even with the most powerful microscopes.
Define an element and give an example.
- Definition: A pure substance composed of identical atoms that cannot be broken down into simpler substances by chemical means.
- Example: Oxygen (O₂)
How are elements different from compounds?
- Elements are made of single types of atoms.
- Compounds are made of different types of atoms chemically bonded together.
What is the Periodic Table?
A chart that organizes all known elements based on their atomic number, electron configuration, and properties.
How many natural elements exist, and how many have been artificially created?
- 92 natural elements.
- 26 artificially created in laboratories.
What categories do elements fall into on the Periodic Table?
- Metals
- Non-metals
- Metalloids based on their properties like conductivity and appearance
What determines an element’s chemical symbol?
It is based on either one or two letters derived from its name.
E.g. H for hydrogen or Na for sodium.
How do elements combine to form substances like water or sugar?
Through chemical bonds.
E.g. water (H₂O) or sugar (C₆H₁₂O₆).
How do electrons affect the properties of an element?
The number and arrangement of electrons determine an element’s reactivity, chemical bonding behavior, and many of its physical properties.
What are isotopes of an element?
These are atoms of the same element with different numbers of neutrons, leading to variations in atomic mass but similar chemical properties.
What are noble gases, and why are they unique?
A group of elements that are typically inert, have full outer electron shells, making them stable and unreactive under normal conditions.
What is the fundamental difference between mixtures and pure substances in chemistry?
- Mixtures: Are composed of substances that are not chemically bonded and can be separated physically.
- Pure substances: have fixed compositions and cannot be separated into simpler substances by physical means.
Examples of pure substances are elements and compounds.
How do compounds differ from elements?
- Compounds are pure substances composed of atoms of two or more different elements in fixed ratios.
- Unlike elements, compounds can be decomposed into their constituent elements through chemical reactions.
What are the types of chemical bonds that hold atoms together in compounds?
- Ionic bonds: Electrostatic attraction between ions of opposite charges.
- Covalent bonds: Sharing of electrons between atoms.
Describe the properties of an ionic compound.
- Formed between metals and nonmetals.
- Have high melting points.
- Conduct electricity when dissolved in water.
- Consist of ions held together by ionic bonds (e.g., NaCl).
Describe the properties of a covalent compound.
- Formed between nonmetals.
- Have lower melting points.
- Do not conduct electricity well.
- Are held together by covalent bonds (e.g., CO₂).
Provide an example of a compound and an element.
- Compound: Carbon dioxide (CO₂), made of carbon and oxygen atoms in a fixed ratio.
- Element: Helium (He), composed of identical helium atoms.
Why are elements reactive and how do they combine to form compounds?
- They are reactive because they seek to complete their electron shells.
- They combine with other elements to form stable compounds through electron transfer (ionic bonds) or electron sharing (covalent bonds).
What role do electrons play in chemical bonding?
They are involved in chemical bonding by either being transferred between atoms (ionic bonding) or shared between atoms (covalent bonding).
This interaction stabilizes atoms into compounds.
How do the properties of compounds differ from those of their constituent elements?
Compounds exhibit properties distinct from their component elements.
For example, sodium (a reactive metal) and chlorine (a toxic gas) combine to form sodium chloride, a stable compound commonly known as table salt.
Explain the difference between molecules and compounds.
- Molecules are formed when two or more atoms bond together, regardless of whether they are the same or different elements.
- Compounds specifically refer to molecules composed of atoms from different elements.
Why are ionic compounds good conductors of electricity when dissolved in water?
They dissociate into ions when dissolved in water, allowing for the free movement of charged particles (ions), which facilitates electrical conductivity.
What is meant by ‘periodic table notation’?
It is a method of presenting the elements, whereby characteristics such as element name, symbol, atomic number, atomic weight, and electron configuration can be easily identified at a glance.
Periodic table notation is used in the periodic table.
When is a subscript used in periodic table notation?
When more than one atom of a particular element is present, subscripts are used to denote the exact number of atoms present.
For example, a molecule of oxygen has two atoms, so it is written as O₂.
By convention, subscripts are always written to the bottom right of the element it is referring to.
What does a chemical formula tell you?
They indicate all the elements within a molecule, as well as the number of atoms of each element.
The chemical formula for methane is CH4. List the number of atoms of each elements present in methane.
Carbon: 1
Hydrogen: 4
When is a coefficient used in periodic table notation?
When there is more than one molecule of a substance, the number of molecules is indicated with a coefficient.
The coefficient is written immediately to the left of the molecule it is referring to. For example, two molecules of water would be written as: 2H₂O.
Define an ion.
It’s an atom or molecule that has gained or lost one or more electrons, resulting in a net electric charge.
An ion has a positive charge if it has lost electrons (cation); a negatively charged ion (anion) results from gaining electrons.
Na+1 is the chemical formula for a sodium ion, which has a positive charge of one unit.
Distinguish between subscripts written on the bottom left and bottom right of the chemical symbol.
Bottom left: Represents the atomic number of the element.
Bottom right: Indicates the number of atoms of the element present in the molecule.
Which image (I, II or III) in the diagram represents a ‘pure substance’?
Image I
This is an element.
